Fix "preload-emulator" command

removed some commands that assumed the emulator was running, and weren't needed either way

stopped doKillEmu() blowing up
return immediately in some situations where adb blocks for a device
add adbSetTarget and adbInitialTarget
check validity of android target before running adb
run ndk-build from jni directory

this causes my jni builds to succeed where they would not previously, but ymmv
update readme
Merge remote-tracking branch 'lustefanik/master' into merged-lustefaniak
restrict scalac to reasonable filename lengths
fix all warnings
bugfixes for adb

synchronize adb bridge setup
correctly handle adb subprocesses producing no output
add preloadAny accepting a user-specified target

internally, most preload methods now take an implicit target rather
than an emulator/not-emulator boolean
Support for sbt version > 0.13.2