Pcre++: rename man page to avoid conflict with pcre.

* The man page of pcre++ is named Pcre.3, while there is one named
  pcre.3 in pcre package. This is problem for case-insensitive file
  system which is widely used across Mac OS X systems. Rename it to
  pcre++ and add caveat about this change.

Closes #21968.
chruby 0.3.7

Closes #21987.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>