vimrc: avoid warnings when editing Perl files.

New versions of Syntastic disable the perl checker by default for security
reasons.  Don't ask to use it unless the appropriate flag is set to avoid
warnings.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
vimrc: enable Syntastic perl checker.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Merge branch 'master' into work