ALLJOYN-2441 Improved the SCons Doxygen Builder

The doxygen builder for SCons now understands how to build the list of
dependencies when building PDF output.

Fixed possible unclosed file pointer error.

Fixed issue that the 'recursive' tag was being read when the 'generate_html'
tag should have been read.

Script now uses the SCons env.Mkdir in place of the python os.mkdir.  This
should fix the issues seen when running this script from cygwin.

To find the PDF builder on windows SCons must be able to find the pdflatex tool
when the environment is created.  For this reason the script now finds all the
environment variables that need to be added to env['PATH'] before creating the
environment and adds them at creation time.

added DOXYGENFLAGS and DOXYGENCOM to the builder to these can be overridden if
needed.

Change-Id: Ie8064d85805b7cf7d39d200afea048199b064f6e
ALLJOYN-2459 Improved performance of whitespace checker on incremental builds

Do not run the whitespace checker on files that have already passed the
whitespace check and have not changed.  This builds a dictionary where
the key is the file name and the value is a sha1 hash.  If the sha1 hash
has not changed between runs then the file will not be checked for
whitespace compliance again.

This will create a file called whitespace.db in the folder SCons was run
from. This file contains the dictionary that will be used each check.

Only a minor performance decrease when doing a clean build. However,
a major performance increase for incremental builds.

Change-Id: I3511fddc9aa507444736e4fe57961a7b59e3c738