Make a backup (filename.old) in editor when saving XML format scenes, layouts or materials, delete after successful save. This prevents losing the file if XML save crashes. Closes #530.
Revert "Allow UIElements to keep their current size if greater than the calculated size during layout updates."

This reverts commit b97c8d4712957a3953fa06e15e89b00d5b15df6d.

FileSelector or the editor's hierarchy window would not resize to smaller properly if the amount of items in the list was being reduced. The MinSize attribute should be used to absolutely prevent layouting making an element smaller.
Add initial support for 64-bit Android ABIs.
For Travis CI - double the time to wait for AVD to start.
AVD with API level 21 seems to take longer to start. Also when the AVD failed to start in time, CI now skips the APK installation/launching test and considers the whole build as passed.
Fix Android toolchain so that Clang always comes after GCC.
Merge some of the changes from one of the android-cmake's PR for NDK r10c.
For Travis CI - attempt to fix failure to start emulator with API 21.
For Travis CI - reduce the AVD waiting time to 1 minutes instead.
There is no point to wait for AVD to start. By the time the CI finishes the build, if the emulator is able to start the AVD then it should have been already done so.
On non-CI environment, the build time could still be much faster than the emulator starting the AVD, thus the function to wait for AVD is still useful in non-CI environment.
Name Android buildvm tool for LuaJIT library differently based on ABI.
Enhance Android related tasks to work with multiple attached devices.
For Travis CI - Fallback to use Lua library for ABI arm64-v8a.
SDK r10c does not ship with the corresponding system image for this ABI yet, so also skip the APK packaging step for now.
Init the URHO3D_64BIT build option to 1 when Android ABI is arm64-v8a.
Fix AngelScript library to support Android ABI x86_64.
Refactor build scripts to auto detect ANDROID and RASPI build options.
Tighten the check to detect Android ABI x86_64 in AngelScript library.
Related to commit b7ab0ad4f8970d52b290b2789a94aefc669b9cfb.
For Travis CI - switch CI build to use Android build environment.