bug#18738: Reference of a uninitialized variable in grep -P

[Norihiro Tanaka]

A variable validated_boundary is used in grep -P.  However, it isn't
initialized correctly.  I found that it causes reference of the
uninitialized variable and wrong result.

  $ echo . | env LC_ALL=C src/grep -P .
  $ echo . | env LC_ALL=en_US.utf8 src/grep -P .

We expect that they return each one line, but return each no line.  Their
test cases are also used to judge whether pcre option is enabled in tests.
So all tests with pcre option will be skipped by the bug.

Sorry, I have no idea to fix the bug.  BTW, the bug isn't reproduced in
grep-2.20 or prior.