system.h: use <usual/ctype.h> instead ctype directly.
system.h: use <usual/ctype.h> instead ctype directly.

Fixes problems with signed chars.

digoal/pgbouncer-x2,dbaxa/pgbouncer,kvap/pgbouncer,digoal/pgbouncer-x2,kvap/pgbouncer,kvap/pgbouncer,wurenny/pgbouncer-x2,jaiminpan/pgbouncer,wurenny/pgbouncer-x2,jaiminpan/pgbouncer,jaiminpan/pgbouncer,dbaxa/pgbouncer,dbaxa/pgbouncer,digoal/pgbouncer-x2,wurenny/pgbouncer-x2,kvap/pgbouncer,wurenny/pgbouncer-x2,dbaxa/pgbouncer,jaiminpan/pgbouncer,digoal/pgbouncer-x2