Delete the file object if the trace file could not be loaded due to being an unsupported (newer) version.

Fix small memory leak / assert if a trace file can't be loaded due to
being recorded with a newer version number than qapitrace. In this
scenario, there is no error message that gets shown in the UI, but the
title bar is updated with the trace file name, so the situation is very
confusing.
Resolve C4267 MS compiler warnings

warning C4267: 'argument' : conversion from 'size_t' to 'unsigned int', possible loss of data
Skip apitrace from FirefoxOS if NDK is not present

Skip apitrace build when compiling FirefoxOS if NDK is not present in
prebuilt/ndk/android-ndk-r7.
Use consistent cpp logic for including backtrace.h

__linux__ -> __ELF__