Arduino 1.5.x - support new library layout and plaform specific system libs

- Add support for 1.5.x library layout.
  (https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification)

- Allow using Arduino 1.5.x platform specific system libraries.
  Arduino 1.5.x has additional directories for platform (vendor/architecture)
  specific libraries - look there when searching for libraries.
Add changelog entry for #275 and #276
remove unwanted TABs
do not print default (empty) ARDUINO_PLATFORM_LIB_PATH value for arduino 1.0.x
Merge pull request #277 from lukasz-e/arduino-1.5.x-libs

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