Add support for debugging ART to the dalvik.gdb script.

This adds two commands:

art-on
art-off

To the gdbclient script for debugging ART-based executables in gdb.
The default is 'art-on'

Bug: 17409881
Change-Id: I90a1aed603e50853a40d5f5ec1c9b168dc17ddc7
(cherry picked from commit 22382a4774d7e7b34cc28082cbe76e58ce48a44b)
Do not call art-on macro by default.

If you are debugging a native process, SIGSEGV gets ignored by default.
The gdbclient bash function has been modified to only call the art-on
macro when running gdbclient app_processXX.

Also, print a warning in case someone is trying to debug a native
process using app_process.

Bug: 17815162
Change-Id: I0666e6713b0a03ee713be7827c5b671938f2c263
(cherry picked from commit 436b740b705c4316d3d5b73f04cdff9b8b8714e8)
Merge changes I0666e671,I90a1aed6

* changes:
  Do not call art-on macro by default.
  Add support for debugging ART to the dalvik.gdb script.