Fixes bug 921248 adding devices and graphics signature summary tables to backfill
Fixes bug 926078 - updates stackwalker

The new stackwalker was updated in HG after we brought it into the
Socorro repo. This ports over those changes from https://hg.mozilla.org/users/tmielczarek_mozilla.com/minidump-stackwalk/rev/b99899ee43c7
Merge pull request #1582 from lonnen/926078-stackwalker

Fixes bug 926078 - updates stackwalker
enhancements to jDump processing - better sentinel detection
Merge pull request #1583 from twobraids/jDump3

Fixes Bug 926507 - enhancements to jDump processing
pep8 ftpscraper, r=AdrianGaudebert
Merge pull request #1557 from selenamarie/bug921248-fix-sigsum-devices-backfill

Fixes bug 921248 adding devices and graphics signature summary tables to...
(no bug) - docs update for GCC requirement

Building MDSW requires GCC 4.6 or greater.
Merge pull request #1584 from lonnen/docs

(no bug) - docs update for GCC requirement