Fix clang warnings about forward definitions

[lehenbauer]

TSP_Util_string_compare_const was forward-declared in TSP_util.c. A trivial reordering declares the function before its first call.

clang on FreeBSD was warning about forward definitions for srand48 and drand48 and this fixes that by importing stdlib.h, which should be pretty safe these days.

[lehenbauer]

Also getting forward declaration warnings for Tcl_PushCallFrame and Tcl_PopCallFrame. Their names seem to indicate they should be defined in tcl.h, but they are defined in tclIntDecls.h.

[lehenbauer]

https://github.com/flightaware/tsp_examples