questions.c

Unify some duplicated code before things get out of sync:

* subversion/include/svn_types.h, subversion/libsvn_subr/validate.c
(svn_mime_type_is_binary): New function.
(svn_mime_type_validate): Renamed from svn_validate_mime_type, so we
have a consistent prefix for mime-type stuff now. All callers
changed.

* subversion/clients/cmdline/feedback.c
(notify): Just call svn_mime_type_is_binary, instead of doing
it by hand.

* subversion/libsvn_wc/questions.c
(svn_wc_has_binary_prop): Same, and users may apply in person for a
refund of the cycles wasted this way.