MFC improvements to bsdinstall's wlanconfig module

MFC improvements to bsdinstall's wlanconfig module

MFC [85] revisions 309719-309720, 309901-309902, 309904-309911,
309913-309920, 309922-309924, 309926, 309928, 309930, 309932, 309934,
309937-309942, 309944-309952, 309958-309998, and 310038 (described below)

r309719: Remove unnecessary trailing backslashes
r309720: Functions in their own section
r309901: Comments
r309902: Use $( ... ) instead of `...`
r309904: Change "[ ! -z ... ]" => "[ ... ]" and "[ -z ... ]" => "[ ! ... ]"
r309905: Remove unnecessary local initializers
r309906: Consolidate locals
r309907: Replace funny block with something easy to digest
r309908: Collapse tiny if statements
r309909: Change "[ ! ... ] && ..." to "[ ... ] || ..."
r309910: Remove unnecessary quotes around number in test
r309911: Group fallbacks together
r309913: Allow $BSDINSTALL_TMPETC to contain whitespace or special chars
r309914: Add missing `-e' parameter to sed invocations
r309915: "echo | sed | sed | awk" is silly (changed to "echo | awk")
r309916: Be internally consistent (": > ..." is used elsewhere in this file)
r309917: awk(1) match() takes a regex, use /.../ to remind ourselves of this
r309918: Remove unnecessary `-n' parameter to head/tail
r309919: Whitespace
r309920: Use provided API instead of hard-coded status integers
r309922: Centralize backtitle string
r309923: There is zero harm in always passing --default-item to dialog
r309924: Always pass --default-item parameter to dialog
r309926: Change the name of a variable from $def_item_... to $default_...
r309928: Use ~ instead of match()
r309930: Use ternary operator
r309932: Remove an unnecessary "return $?" at end of function
r309934: Consolidate redirects into here documents
r309937: Whitespace (dialog options separated to minimize diffs)
r309938: Use provided API (change "dialog" to "$DIALOG")
r309939: Fix incorrect use of provided API
r309940: Reorder dialog parameters based on commonality for readability
r309941: Use provided API to centralize dialog title strings
r309942: Allow the script path to contain whitespace and special characters
r309944: Fix invalid parameter expansion (change $@ to "$@")
r309945: 1 is the default descriptor for redirects without an fd prefix
r309946: Use more succinct awk syntax
r309947: Remove unnecessary semi-colons
r309948: Remove incomplete and unnecessary creation of fd3
r309949: Utilize provided i18n strings
r309950: Whitespace
r309951: Remove an unnecessary call to f_dialog_title_restore()
r309952: Move the secondary condition into the action clause
r309958: Quote WLAN_IFACE (pedantic)
r309959: Use oft-neglected syntax "startcondition, stopcondition { ... }"
r309960: Add missing backslash
r309961: Stop repeating strings (centralize prompt string)
r309962: More efficiently make use of the exit status
r309963: Avoid non-standard options
r309964: Sort the domains
r309965: Whitespace alignment
r309966: Sanitize dialog output for portability/compatibility requirements
r309967: Use more generic f_yesno() from provided API
r309968: Properly quote variable
r309969: Send stderr to the same place as stdout
r309970: Remove completely unnecesary parentheses
r309971: Start deconstructing a conveluted hunk of code
r309972: If the first ping succeeded, why on Earth should we ping it again?
r309973: Why use $? when you can use the command itself
r309974: These two error messages have always been backwards since inception
r309975: Continued resolution of conveluted statement
r309976: You don't need parentheses for awk's printf
r309977: Whitespace and alignment
r309978: Neither printf nor print need parens in awk
r309979: This statement has too many backslashes
r309980: Just use print
r309981: Add missing quotes
r309982: Remove unnecessary quotes
r309983: Use the provided API for calculating the appropriate size of menus
r309984: Whitespace alignment
r309985: Comment
r309986: There's an API function for displaying errors
r309987: There's an API function for displaying yes/no dialogs
r309988: There's an API function for displaying pauses
r309989: There's an API function for catching errors
r309990: Calculate proper size of menu list dialog
r309991: Simplify bringup of interface after changes and catch errors
r309992: Restore previous comment
r309993: Why test $? when you can test the command
r309994: Wordsmithing
r309995: Simplify loop by moving predicate to clause
r309996: Simplify single-line if statements
r309997: The flags of a WLAN need to be quoted
r309998: It's completely pointless to replace newlines with space
r310038: Revert r309918 -- modern POSIX has deprecated -<#>/+<#> syntax

PR:		bin/214933