Add TypedConfigGetter.getPath()

Add TypedConfigGetter.getPath()

This enables EGit to override with a lenient variant that logs the
problem and continues with the default value. EGit needs this because
otherwise a corrupt core.excludesFile entry can render the whole UI
unusable (until the git config is fixed) because any use of the
WorkingTreeIterator will throw an InvalidPathException.

This is not a problem on OS X, where all characters are allowed in
file names. But on Windows some characters are forbidden... see bug
567296. The message of the InvalidPathException is not helpful since
it doesn't point to the origin of the problem. EGit can log a much
better message indicating the offending config file and entry in the
Eclipse error log, where the user can see it.

Bug: 567309
Change-Id: I4e57afa715ff3aaa52cd04b5733f69e53af5b1e0
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>