Prevent creation of invalid git config keys
Allow only alphanumeric characters and the dash in git config
section and variable names. Subsections get quoted and may contain
other characters.
Extend the validation in AddConfigEntryDialog to prevent the
accidental creation of invalid git config entries; those would
break all git, JGit, and EGit functionality and the only way to
fix this would be to edit the offending git config file manually
in a text editor. With an invalid git config file, not even
"git config --help" works!
Change-Id: I65a3279069639d44922da8c8792a27b9aa51fe4e
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>