Refine SConstruct `BOOST_APPEND` setting.

[jbronn]

When specifying BOOST_TOOLKIT the -mt flag was being put in the wrong order -- this fixes that. Moreover, the -mt flag and BOOST_TOOLKIT setting are set once in BOOST_APPEND, which is then subsequently used by the dependency routines. I've also added in some autodection logic for Boost 1.35 so that the extra dependencies for OSX are automatically added (is this required for any other platforms w/1.35 or must OSX?).

I've successfully tested (rundemo.py) with both debug and non-debug builds on OSX 10.5 using both Boost 1.34.1 and 1.35.

[jbronn]

Fix for compiling mapnik on OSX with Boost 1.35.

[jbronn]

Updated version of this patch, refines BOOST_APPEND further by using correct ordering of components.

[jbronn]

The BOOST_TOOLKIT compile time setting is not enough. In order to allow construction of the Boost libraries you have to take into account toolkit, version, and abi flag. The second version corrects the Boost library naming scheme and updates for latest mapnik version.

Thus, when helping out those trying to install it will as simple as instructing them to add BOOST_VERSION=1_35 BOOST_TOOLKIT=gcc to their scons line.

[jbronn]

Updated so that patch applies cleanly after changes in r748.