scripts/get_maintainer.pl: better email routines, use perl not shell where possible

Added format_email and parse_email routines to reduce inline use.

Added email_address_inuse to eliminate multiple maintainer entries
for the same email address, the first name encountered is used.

Used internal perl equivalents of shell cmd use of grep|cut|sort|uniq

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>