Don't add duplicate shortcuts to the accelerator table.
Use memcmp suggested in review feedback.
Merge pull request #426 from adobe/rlim/handle-accel-table

Don't add duplicate shortcuts to the accelerator table.
Merge branch 'master' into jeff/cef_1750
Merge branch 'jeff/cef_1750' of https://github.com/adobe/brackets-shell into jeff/cef_1750