chicken-install cache doesn't respect isolation

[alicemaz]

the directory name "chicken-install" is hardcoded in egg-environment.scm. this patch uses the name of the chicken-install binary instead, so that different versions of chicken built with PROGRAM_PREFIX or PROGRAM_SUFFIX have separate caches

different versions with different install locations but the same program names still overlap, but they would overlap in PATH anyway, so this doesn't strike me as a big deal. program prefix/suffix is intended to allow complete isolation of multiple builds tho so separating caches feels obviously correct. (in my own case, I use my distro's packaged chicken for most day-to-day work alongside a prefixed install built from git for messing with chicken itself)

the CHICKEN_EGG_CACHE env var still overrides the default cache location unconditionally, which also seems correct even if it allows multiple versions' caches to merge, since the point of env vars is to enforce something system-wide in all cases invariably

tested on platform=LINUX

[sjamaan]

Fixed in d61fb34c21