Major fixes:
 - The "Select Boost Options" was improved:
   - In previous versions, it was possible to unselect both Shared and Static
     options, so that there would be nothing to be built. This was solved by
     creating a choice menu "Compile Boost libraries".
   - A new choice menu was also created for Boost Run-time linkage called
     "Selects Boost Run-time linkage", which is used to select the C and C++
     runtime. This choice menu obeys to the required restrictions by boost
     options [1].

 - Fixed the invalid combination where boost shared version could be linked
   to C and C++ static runtime. This is not allowed by the boost builder.
 - Added new menu where a Boost building variant can be chosen from 3 options:
   - Release: The optimized version for daily use.
   - Debug: The debugging version, for testing purposes.
   - Profiling: The profiling version for evaluation purposes.
 - Improved options help descriptions.

Minor fixes:
 - Makefile Version was bumped from 6 to 8 because the previous update [2] did
   not bumped the value acordingly to the submission rules.
 - Removed stuff that was not doing anything: "-sBUILD=release"
 - Changed builder executable from "bjam" to "b2" which is the correct caller:
   - "bjam" is the old name and exists only for compatibility purposes.

[1]: http://www.boost.org/build/doc/html/bbv2/overview/builtins/features.html
[2]: openwrt#2084

Signed-off-by: Carlos M. Ferreira <carlosmf.pt@gmail.com>