scripts/get_maintainer.pl: add default --git-fallback, remove default --git

scripts/get_maintainer.pl: add default --git-fallback, remove default --git

Adding commit signers when there is a listed MAINTAINER for a file
can make the output list longer than necessary.

Change the --git default from on to off.

Add a new --git-fallback option (default on) used to add commit signers
only when there is no MAINTAINER for a file.

git history is used when --git-fallback is enabled and the pattern
directory depth is not the same as the file directory depth.

For instance:

X86 ARCHITECTURE (32-BIT AND 64-BIT)
M:	Thomas Gleixner <tglx@linutronix.de>
M:	Ingo Molnar <mingo@redhat.com>
M:	"H. Peter Anvin" <hpa@zytor.com>
M:	x86@kernel.org
T:	git git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-x86.git
S:	Maintained
F:	Documentation/x86/
F:	arch/x86/

If using "./scripts/get_maintainer -f arch/x86/lib/atomic64_32.c", the pattern
for "arch/x86/" does not match the directory depth of "arch/x86/lib"
so the MAINTAINERS entries and git history is used to produce:

$ ./scripts/get_maintainer.pl -f --rolestats arch/x86/lib/atomic64_32.c
Thomas Gleixner <tglx@linutronix.de> (maintainer:X86 ARCHITECTURE...)
Ingo Molnar <mingo@redhat.com> (maintainer:X86 ARCHITECTURE...)
"H. Peter Anvin" <hpa@zytor.com> (maintainer:X86 ARCHITECTURE...,commit_signer:1/1=100%)
x86@kernel.org (maintainer:X86 ARCHITECTURE...)
Luca Barbieri <luca@luca-barbieri.com> (commit_signer:1/1=100%)
linux-kernel@vger.kernel.org (open list)

Luca Barbieri is added because he signed the only commit to
arch/x86/lib/atomic64_32.c during the last year and he meets the
other default qualifications.
	--git-min-percent (default:10)
	--git-min-signatures (default:1)

If current users of ./scripts/get_maintainers.pl have scripts
that use --nogit that expect git history to be excluded, those
scripts should be updated to include --nogit-fallback or a
.get_maintainer.conf file should be created with --nogit-fallback.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>