Compilation errors when switching from --test to checking main

[alastairreid]

Switching back and forth between 'cargo-verify --tests' and 'cargo-verify ' causes compilation error problems.
The problem is that it is hard to predict the exact name of the bitcode file generated on different systems under different compilation commands so 'cargo-verify' uses an overly liberal glob to find the file.

For now, the workaround is to run cargo clean to remove old files.
The right fix is probably to get cargo to report the actual filename that we need.

[alastairreid]

Although it does not fix the problem, I have added a "--clean" flag to cargo-verify to make it a little easier to do a clean reverification