Comal: Support non-constant string lengths in DIM...OF

[stevewpalmer]

The current syntax for DIM with strings is:

DIM string$ OF <constant>

However the Comal specification allows the use of a computed expression in place of <constant>. At present we handle allocation of strings in a static manner due to the constant size so this would require the implementation of dynamic length strings which is not supported in JComLib at present.

See the slp.lst sample and this line:

1080   DIM alloc$ OF blksize#

for an example.