New command ggtags-visit-project-root using key C-c M-j

Initialise ggtags-project-root to 'unset so that
ggtags-highlight-tag-at-point is run automatically.

Remove all compiler warnings for emacs 24.1-trunk.
Don't let deleting text screw up compilation-filter-start
Avoid "--regexp" and use "--" instead

Extend ggtags-find-tag to support arbitrary arguments and callers
changed.
Make use of colored output to calulate column

and enable it for grep and ctags-x output formats.

The cscope output format doesn't include leading blank from the source
text so cannot calculate column without support from compile.