hgmerge: fix diff+patch detection; cleanups
Details:
- actually show help message when no tools are found
- whitespace cleanup (stupid emacs)
- quote more variables
- simplify merge/diff3 error handling
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory