Fixed error message generation in PFDEBUG GETREG.

Bulk length for registers was emitted too early, so if there was a bug
the reply looked like a long array with just one element, blocking the
client as result.
hllSparseAdd() opcode seek stop condition fixed.
More robust HLL_SPARSE macros protecting 'p' with parens.

Now the macros will work with arguments such as "ptr+1".
Merge adjacent VAL opcodes in hllSparseAdd().

As more values are added splitting ZERO or XZERO opcodes, try to merge
adjacent VAL opcodes if they have the same value.