MFC r246134 ...

MFC r246134 ...

Improve devd startup time, by tweaking some string handling routines that are
heavily used when parsing config files.  Mostly these changes avoid making
temporary copies of the strings, and avoid doing byte at a time append
operations, on the most-used code path.

On a 1.2 GHz ARM processor this reduces the time to parse the config files
from 13 to 6 seconds.

git-svn-id: svn://svn.freebsd.org/base/stable/9@247803 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f