update checkpatch.pl to version 0.18

This version brings a few fixes for the extern checks, and a couple of
new checks.

Of note:
 - false is now recognised as a 0 assignment in static/external
   assignments,
 - printf format strings including %L are reported,
 - a number of fixes for the extern in .c file detector which had
   temporarily lost its ability to detect variables; undetected due to
   the loss of its test.

Andy Whitcroft (8):
      Version: 0.18
      false should trip 0 assignment checks
      tests: reinstate missing tests
      tests: allow specification of the file extension for a test
      fix extern checks for variables
      check for and report %Lu, %Ld, and %Li
      ensure we only start a statement on lines with some content
      extern spacing

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>