porting to 4.8.*

[Dmitrii Pasechnik]

it will need

1. generation of gap_version.h done by the updated GAP build system (by make, after it builds (if needed) GMP...)

2. update of generation of config.h, which now generates HAVE_GETTIMEOFDAY and HAVE_GETRUSAGE (which are autoconf macros)

[Dmitrii Pasechnik]

I ended up making the following src/gap_version.h by hand

#ifndef GAP_BUILD_VERSION
#define GAP_BUILD_VERSION  "libgap-4.8.1"
#define GAP_BUILD_DATETIME "2016-01-14 17:40:33 (GMT)"
#endif

GAP generates this file during build and puts it in bin/<arch>.... (libGAP_ prefixes will be added then by the script)