New & improved man page attached, now with standard license added.

Plus, a patch for scan-build.  

* mdoc corrections
* slightly more compact output
* same license as scan-build
* DESCRIPTION describes
* Default checkers corrected & explained
* Authors credited

The patch adds support for --help-checkers.  It just lists the default
checkers by recursively invoking "scan-build -h" and looking for the
magic '+' signs.  

Patch by James Lowden!

llvm-svn: 157411