--lcov-web-all crashes after the second report is finished

[MarkusTeufelberger]

Python complains that the file "lcov-web-final.html" already exists and kills the whole program, as soon as genhtml finishes the second report (around line 600).

http://stackoverflow.com/a/27103129 has a nice short function to fix this issue that works beautifully as a drop-in replacement.

[Michael Rash]

Please let me know if you see any additional issues with this fix.