[VFP dialect] Compatibility: Add an IN clause to the USE command

[vfp9]

The USE command already exists in X# and the NEW clause is valid. However, in VFP, the command that accomplishes the same thing is

*!* 0 is the next available work area 
Use XXX.DBF In 0

In VFP, tables can also be opened in different work area depending on the number in the IN clause, for example:

*!* Open the table in the third work area
Use XXX.DBF In 3

or

*!* abc is an alias for the work area, which may also be XXX
Use XXX.DBF In abc

Note: If numbers are used, then the alias of the work area where the table is opened should default to the table name.

[RobertvanderHulst]

See #1527