whereis: reset search mask more carefully

whereis: reset search mask more carefully

 # whereis -m cal -M /usr/share/man/man1/ -f ls
 cal: /usr/share/man/man1/cal.1.gz /usr/share/man/man1p/cal.1p.gz
 ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

the -M also resets the search mask, so for 'ls' it returns also
binaries. That's bug. Expected result is:

 # ./whereis -m cal -M /usr/share/man/man1/ -f ls
 cal: /usr/share/man/man1/cal.1.gz /usr/share/man/man1p/cal.1p.gz
 ls: /usr/share/man/man1/ls.1.gz

the search mask has to be sensitive only to -b -m -s options,
otherwise the semantic is pretty messy.

Signed-off-by: Karel Zak <kzak@redhat.com>