Fix missing line number information in errors encountered during 'for' prep
Fix missing line number information in errors encountered during 'for' prep

SharpLua has a modified implementation of the OP_TFORLOOP opcode, containing
an additional code path (why?)  This alternate code path did not set savedpc,
which caused line number information to not be correctly propagated if the
arguments to 'for' are incorrect.

Failing test:

slua -e "print(pcall(loadstring('\n local a \n for k,v in 3 \n do \n print(k) \n end')))"

Stevie-O/SharpLua,Stevie-O/SharpLua,Stevie-O/SharpLua