Bootstrap.mak clean target(s)
Bootstrap.mak clean target(s)

Bootstrap can now clean itself using make -f Bootstrap.mak <platform>-clean

* Factorize cleanup tasks in two targets
	* windows-clean for windows systems
	* nix-clean: For all UNIX-based systems
* Add a "*-clean" target counterpart for each target as an alias of windows-clean or nix-clean
* Make each target invoke its *-clean target before running
* Replace use of $? / $** by explicit $(SRC) in build rules
	They cannot be used anymore due to the presence of the *-clean target in dependency list

starkos/premake-core,premake/premake-core,dcourtois/premake-core,starkos/premake-core,starkos/premake-core,starkos/premake-core,dcourtois/premake-core,premake/premake-core,starkos/premake-core,dcourtois/premake-core,premake/premake-core,premake/premake-core,dcourtois/premake-core,noresources/premake-core,dcourtois/premake-core,premake/premake-core,noresources/premake-core,starkos/premake-core,noresources/premake-core,noresources/premake-core,noresources/premake-core,premake/premake-core,dcourtois/premake-core,dcourtois/premake-core,starkos/premake-core,noresources/premake-core,noresources/premake-core,premake/premake-core