[cvsnt] cvs diff -I broken in 2.0.51

[Mark Levedahl]

cvs diff -Ifoo should suppress any diff lines containing 'foo' (which can be
a regular expression). This works fine in 2.0.35, does not work in 2.0.51a,
have no idea what version actually broke it.

Example of current symptoms:

cvs diff -Ifoo  suppresses everything if foo is not matched.
cvs diff -Ifoo causes a crash in cvs if foo is matched.

Mark Levedahl