fix debug build use of dbg_printf in fping.c

fix debug build use of dbg_printf in fping.c

config.h must be include before fping.h, because
configure --enable-debug writes the DEBUG #define
to config.h, and the dbg_printf macro definition
requires a defined DEBUG to actually produce any
output.

Unbreaking dbg_printf() exposed an instance of
wrong use, so fix that.  Also, add a newline to
the debug output reporting used CPU time.