TBR: DrMi#1795 drreg: add drreg_restore_app_values()

Commit log for first patchset:
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DrMi#1795 drreg: add drreg_restore_app_values()

Dr. Memory's in-progress conversion to use drreg has exposed a few missing
features: when restoring app values, all spilled registers are not
necessarily known as other components than the current code could have
spilled some.  With drreg's lazy restores, a routine to restore *all*
registers used by an operand is needed.  We add drreg_restore_app_values()
for this purpose.

Adds a few tests as well.
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[bruening, 2017-01-18 04:56:52]

Committed as
https://github.com/DynamoRIO/dynamorio/commit/3479fcb277b181077c63ac4208c363d...

Final commit log: 
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DrMi#1795 drreg: add drreg_restore_app_values()

Dr. Memory's in-progress conversion to use drreg has exposed a few missing
features: when restoring app values, all spilled registers are not
necessarily known as other components than the current code could have
spilled some.  With drreg's lazy restores, a routine to restore *all*
registers used by an operand is needed.  We add drreg_restore_app_values()
for this purpose.

Adds a few tests as well.

Review-URL: https://codereview.appspot.com/320000043
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