gitignore: Return lines for ignoring autoconf generated files.
CMakeLists.txt: Set cmake policy CMP0018 to OLD.

Needed for compatibility with cmake 2.8.9 and higher.
See: http://www.manpagez.com/man/1/cmakepolicies/
plugins/optimizations: Rename Makefile to Makefile.in
plugins/spells: Ignore unused variable error.
plugins/connect: Add -Wno-return-type to CMAKE_CXX_FLAGS

Ignore the return type errors from the v2.8 api.
plugins/fixes: Add -Wno-return-type to CMAKE_CXX_FLAGS

Ignore the no return value errors from v2.8 api.
install.sh: Bug fixes.

- Script was adding 'plugins/$plugins' to
  extraplugins string which when passed to configure
  would then also add 'plugins/' and would attempt to find
  'plugins/plugins/$plugin'.

- Test for file existance doesn't support wildcards and so was
  throwing an unexpected command error when attempting to
  concatenate plugin specific nwnx2.ini files.
Merge pull request #1 from jd28/build-issues

Fix a few build issues.