add revision numbers to urdf defs files (ros ticket #2788)

[ahendrix]

Suffix all pr2_defs/defs files by _vN where N is an integer number starting at 0.

for example head_defs_v0.urdf.xacro

trac data:

• Owner: hsu
• Reporter: hsu
• Reported at: Wed Sep 16 16:53:23 2009
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/2788

[ahendrix]

[hsu] continue work in package pr2_description.

Not sure how to address multiple revisions of the same part (macro) on one robot.