gltrace: Prefer process title over executable path on Android

v2: Add comment (Jose Fonseca)
md5: Fix include for memcpy.

It should be string.h.  This fixes warnings about undeclared memcpy
when building for Android.
Use /data/data/$procname/$procname.trace on Android

So that applications with apitrace built-in with WRITE_EXTERNAL_STORAGE
permission can write traces on non-rooted devices too.

See issue #149.