Normalise indentation and remove all trailing whitespace. No functional changes.
Remove xfree, as any respectable compiler (i.e. one that follows the C standard) won't crash if you call free(3) on NULL.
Provide a macro to make debug messages much nicer.

This updates messages to display logs like so:
    squidclamav.c(252) squidclamav_close_service: DEBUG clean all memory!

This makes debugging both nicer to read and write.
Remove unused variable