Fix variables defined in macros appearing multiple times in the Navigation pane.
See https://bugzilla.mozilla.org/show_bug.cgi?id=956855
Add comment describing the use of -1 to mean "no extent"
Document source_encoding setting.

Fix a few others after digging into the config module source.
Add compatibility for clang 3.5 (svn)
- FunctionDecl::getResultType() was renamed to FunctionDecl::getCallResultType()
- We were misusing DiagnosticsEngine::getCustomDiagID as it should always
  take a constant string.  Switch to using formatted output to make this work
  on both clang 3.5 and previous versions.
- Correct a copy-paste error where we were printing the name of the output
  directory instead of the name of the temporary directory in an error
  message.
Merge pull request #290 from abbeyj/clang-3.5

Add compatibility for clang 3.5 (svn)