Fix strncat build warnings when building with gcc.

[sprintersb]

There are several places where suspect len arguments to strncat are specified, like for example in mylib/gdef.c::gdef_GetHostName():

   strncat (machine, ", ", (size_t) 2);

The semantics of strncat is that it writes at most 2 chars from ", " plus an additional terminating '\0' as needed. This is 3 chars, presumably what the authors intended. The obvious approach here would be to just use strcat for small static strings like in the sample, though the patch keeps the current coding style with strncat.

* mylib/gdef.c (gdef_GetHostName): Use proper len specification in strncat calls, i.e. pass the size of the source rather than the length.
* testu01/ubrent.c (ubrent_CreateXorgen64): Same.
* testu01/ulec.c (ulec_CreateMRG31k3p): Same.
* testu01/unif01.c (unif01_CreateLacGen,  unif01_CreateBiasGen) (unif01_CreateDoubleGen2, unif01_CreateDoubleGen): Same.
* testu01/svaria.c (svaria_SumLogs, svaria_WeightDistrib) (svaria_CollisionArgMax_00, svaria_SumCollector): When writing to chaine[], use the length of chaine[], i.e. LEN1 in strncat, instead of LEN2 which exceeds the length of chaine[].