Command line option for disabling warnings

This commit adds a new command line option to dx:
--no-warning.
If the caller appends this to the arguments, dx won't print
warnings to System.err. This can be useful if the user
dexes external jars with old class format, so dx would
print lot of warning about those.

Bug: https://code.google.com/p/android/issues/detail?id=78285

Change-Id: Ic2da274ec72e096bcf871c1f4512c54ddc228721
Signed-off-by: Csaba Kozák <kozakcsabi@gmail.com>
Merge "Command line option for disabling warnings"