[gpm]minor bugs in 1.20.0

[Alessandro Rubini]

Looking for gpm_oops() in 1.20.0, I found the following:

* gpm.h declares prototypes for tools.c functions, but they should
be in gpmInt.h instead (tools.c is not in the library, it's internal
to gpm instead).

* gpm_oops is said to be in tools.c but it isn't there.

* Gpm_cnt_digits is really hairy. Especially given that it's only used
to malloc the console name. Since consoles are limited to 64 you can
just use 2 (or three, to be safe; the lost byte is definitely less
than the overhead of two functions, one of them recursive).