checkpoint for volodya

svn path=/branches/bbv2python/boost/tools/build/v2/; revision=37161
gcc.jam: build and use import libraries on Cygwin and Windows, but
         accept DLL-only linking with prebuilt DLLs.

builtin.jam: fix default-host-os so that <target-os> actually becomes
             a functional feature.  Improve English in comments

property-set.jam: add str method so we can print them in generator
                  debugging output.

generators.jam: improved debugging output

build-system.jam: add missing semicolon

svn path=/branches/bbv2python/boost/tools/build/v2/; revision=37162
Fix a bug in my DRY refactoring

svn path=/branches/bbv2python/boost/tools/build/v2/; revision=37163
python.jam
----------

* Removed comments about known problems because they make no sense.

* Unified MacOS initialization with NT and *nix

* Updated comment describing init behavior

* Support for passing Python command as first argument

* Removed unused get-python-interpreter and get-python-version rules,
  since they can't work with that interface.  Working versions of
  these will be reinstated for Doug Gregor in the near future.

* When invoking Python to collect configuration info, collect it all at at once.

* When a Cygwin symlink is found by an NT build of bjam, give hints
  about where to find the file it points at.

* Lots of refactoring

* Make the logic work plausibly even when no Python executable can be found


darwin.jam
----------

* Simplified logic for setting up FRAMEWORK_PATH

* Corrected logic for setting up -framework option


feature.jam
-----------

* Make feature.defaults, feature.attributes, feature.values, and
  feature.get-values resilient to feature names being passed without
  grist.


gcc.jam, python.jam, builtin.jam
--------------------------------

* Include some progress volodya has made toward support for <suppress-import-lib>

svn path=/branches/bbv2python/boost/tools/build/v2/; revision=37176
python.jam:
* fix cross-NT/CYGWIN build support
* add condition to the build requirements of the python targets

os.jam:
* add the ability to get constants for a particular OS

builtin.jam:
* remove "optional" attribute from host-os
* fix confusing indents

svn path=/branches/bbv2python/boost/tools/build/v2/; revision=37185