Merge android-port & kernel-cache feature

Android port for merge

Major changes are in enabling kernel-cache
pocl_util.c : 
pocl_choose_dir() - chooses root folder for caching
pocl_create_source_dirs() - searches for matching program in sub-directories
other changes are either retaining files for caching or deleting unwanted files after cmpilation
use /sys/devices/system/cpu/possible file to find num-cores. Some android kernel shows no processor info on /proc/cpuinfo
plus pocl-android-sample in examples/
It's legal to have white spaces after the hash mark. Thus, "#   include" would bypass the cache invalidation in this case. Hopefully there's a fast enough way to alleviate this problem. The best way, of course, would be to use preprocessed sources.