- Several details in 'lcode.c'
- A few more tests for code generation
- Bug in assert in 'lcode.c' ("=" x "==")
- Comments in 'lopcodes.h' and 'ltable.c'

- The preprocessor must work with at least 'long', and therefore must
do shifts of up to 31 bits correctly.
- Whenever possible, use unsigned types in shifts.

Checks of the form '1 <= x && x <= M' were rewritten in the form
'(unsigned)x - 1 < (unsigned)M', which is usually more efficient.
(Other similar checks have similar translations.) Although
some compilers do these optimizations, that does not happen
for all compilers or all cases.

Version numbers and dates (mostly wrong) from RCS keyword strings
removed from all source files; only the file name are kept.

be used as a hint for '#t'

(instead, use a different kind of nil to signal the fake entry returned
when a key is not found in a table)

(used only in errors for now)

rttype -> rawtt; ttyperaw -> withvariant; ttype -> ttypetag;
tnov -> ttype