[analyzer] Run post-stmt checks for DeclStmt.

No tests because no in-tree checkers use this, but that shouldn't stop
out-of-tree checkers.

Found by Aemon Cannon!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190650 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Fix copy-paste error in internal docs.

Patch by Jared Grubb!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190651 91177308-0d34-0410-b5e6-96231b3b80d8
Fix two incorrect comments.

Patch by Jared Grubb!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190652 91177308-0d34-0410-b5e6-96231b3b80d8