libproc: Match prefixes when looking up mapped object by name.

libproc: Match prefixes when looking up mapped object by name.

When looking up an object by name, allow prefix matches if no direct match
is found. This allows one to, for example, match libc entry probes with:

 # dtrace -n 'pid$target:libc.so::entry' -c ./foo

instead of requiring "libc.so.7" or a glob.

Also remove proc_obj2map() as it currently just duplicates the
functionality of proc_name2map(). It's supposed to take a Solaris
link-map ID as a paramter, but support for this isn't implemented and
isn't required to support DTrace's pid provider.