Implements ticket:401 and ticket:402.

Implements ticket:401 and ticket:402.

Adds several API functions to determine build constants at runtime, and
a convenience command line program to display them:

From C++:

const std::string gr_prefix();
const std::string gr_sysconfdir();
const std::string gr_prefsdir();
const std::string gr_build_date();
const std::string gr_svn_date();
const std::string gr_svn_version();
const std::string gr_version();

From Python:

gr.prefix()
gr.sysconfdir()
gr.prefsdir()
gr.build_date()
gr.svn_date()
gr.svn_version()
gr.version()

The new binary is 'gnuradio' and installed on the path:

$ gnuradio
Program options: gnuradio [options]:
  -h [ --help ]         print help message
  --prefix              print gnuradio installation prefix
  --sysconfdir          print gnuradio system configuration directory
  --prefsdir            print gnuradio preferences directory
  --builddate           print gnuradio build date (RFC2822 format)
  -v [ --version ]      print gnuradio version
  --svnversion          print SVN repository version (SVN format)
  --svndate             print SVN repository date
$

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@11418 221aa14e-8319-0410-a670-987f0aec2ac5