checkpatch: improve tests for fixes:, long lines and stack dumps in commit log

Including BUG and stack dumps in commit logs makes checkpatch produce some
false positive warning messages.

checkpatch has multiple types of false positives:

o Commit message lines > 75 chars
o Stack dump address are mistaken for git commit IDs
o Link: and Fixes: lines are allowed to be > 75 chars.
o Fixes: style doesn't require ("<commit_description>")
  parentheses and double quotes like other uses of
  git commit ID and description.

Fix these.

Miscellanea:

o Move the test for checking $commit_log_possible_stack_dump
  above the test for a long line commit message
o Add test for hex address surrounded by square or angle brackets

Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>