Fix bsdgrep manpage clobbering grep(1) with default build options

Fix bsdgrep manpage clobbering grep(1) with default build options

The default build should install bsdgrep(1) and grep(1), with the latter
being gnugrep(1). WITH_BSD_GREP flips this situation such that we have
gnugrep(1) and grep(1), with the latter being bsdgrep(1).

Changes to start installing the zgrep script out of usr.bin/grep
inadvertently altered the default build such that grep(1) was being
installed, and it was bsdgrep(1). Correct the typo.

Reported by:	bcran
MFC after:	3 days