Added a long-winded comment (and commented-out comment to go with out)

about how it would be nice to write absolute paths to the temporary
byte-compilation script, but this doesn't work because it screws up the
trailing-slash trickery done to 'prefix' in build_py's 'byte_compile()'
method.

Fixed to use 'execute()' instead of 'os.remove()' to remove the temporary
script: now it doesn't blow up in dry-run mode!