New compiler and bytecodes for foreach and lmap: 70% faster

* speed as measured by http://wiki.tcl.tk/39021: runs in <1/3 the time
  the time
* still need to adapt array-set to use this
* assemble.test-16.5 or 16.6 bombs in a purify/symbols build (?)
* removing the old opcodes would force old .tbc files to be recompiled, or
  an adaptation of tbcload to rwrite all foreachs
add comments on field "misuse"
add comments on INST_FOREACH_*
tighter mem management
tighter mem management in array-set compiler
adapted the array-set compiler to use the new foreach opcodes
3x speed improvement in foreach, via new compiler and opcodes. The old version remains for old .tbc sake, but is unused in the core.