Bad idea: Lookup actual HugeTLB page size via /proc/self/pagemap.

Bad idea because it doesn't work: the file reports 4096 even for huge
pages. Committed just in case this code should be dug up some day for
some other purpose.

The next commits will rollback these changes and add a better solution.
Revert "Bad idea: Lookup actual HugeTLB page size via /proc/self/pagemap."

This reverts commit 03c248c1a9a9e1f563f4fb923a2b4c5f7920bf06.
lib.lua: Added readfile() and writefile().
memory.lua: Lookup HugeTLB size by groveling /proc/meminfo.

Had been an unreliable constant.