Arduino 1.5.x libs - handle new library layout (issue #275) and hardware/vendor specific libs (issue #276)  

My 3 cents for full arduino 1.5.x support (issue #45):
- (issue #276) when arduino 1.5.x is detected, additional path is searched for hardware/vendor specific libraries (aka $(ARDUINO_PLATFORM_LIB_PATH) ) - defaults to $(ARDUINO_DIR)/hardware/arduine/$(ARCHITECTURE)

- (issue #275) support for new arduino library layout, as specified in https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification .
New layout is assumed when there are library.properties file and src subdirectory in library directory.
In new layout mode src subdirectory is searched recursively for library sources (using rwildcard)

- additional small thing allowing compiling 1.5.x libraries - define ARDUINO_ARCH_XXX when compiling (needed for system libraries in 1.5.x)

(Tested in arduino 1.0.5 and current ide-1.5.x branch )

if you look at the PR discussion rather than this line note, i proposed a diff that doesn't print on 1.0 if empty, although it would still print if it was explicitly set on 1.0 even though its not used, which is probably ok.

the alternative is to move the version check line upwards, with the ```ifndef ARDUINO_PLATFORM_LIB_PATH``` line inside the ifeq, but not sure about that either.