This function is similar to LOOKUP%, except it does not suffer with any problems under SMS.
If the specified name$ does not exist, -12 is returned. -7 is returned if there is some mismatch between table entries.
A file called TurboFix_bin can be used to allow BASIC_INDEX% to access the Minerva MultiBASIC and SMS SBASIC name tables. Some early versions of TurboFix_bin have bugs in it. Beware that not all versions of this file supports SMS SBASICs.