Fail in the release script on lightweight tags.

Also warn on improper code signing and clean up formatting.
Use precompiled code sign requirements to keep compatibility with 10.5+.

Note: code sign requirements must be compiled on 10.5 to be compatible with it.
Make sure our xml is valid.
No quotes in xcconfigs.
keys/ --> signing/
Merge pull request #124 from dak180/topic/build-system

Build System Refinements.