take care of proper PATH and error handling

add dependencies and build scripts to be able to build all configurations from the solution SparkleShare.sln
the used git binaries are now built from source

build configurations are now:

Debug: with debug symbols and symbol DEBUG defined
Release: without debug symbols, with optimizations, depends on installed Mono framework
ReleaseDist: like Release, but all depending frameworks are merged into one OSX binary, installed Mono framework not needed / used