make sys/param.h not depend on PATH_MAX and NAME_MAX

make sys/param.h not depend on PATH_MAX and NAME_MAX

this is a nonstandard header used only by backwards programs, but for
some reason it's extremely popular. the recent namespace cleanup fixes
broke it, because PATH_MAX and NAME_MAX will not be defined unless an
approriate feature test macro has been defined. moreover, it's too
late to just #define _GNU_SOURCE in param.h, since limits.h may have
already been included.

let's just hard-code standard values and be done with it.