resurrecting Bud and Rebuild

[Walter Bright]

It was (correctly) pointed out that textual import breaks Bud and 
Rebuild. It's also been pointed out that textual import may be an 
unexpected vector for security problems.

Both can be resolved by only allowing textual import if a command 
switch, say, -Jpath, is given. 'path' gives the location of where to 
look for the file; and the file will be restricted to being under that 
path. No -Jpath, and textual import won't be allowed.

For Bud and Rebuild, if there's no -J, they know there are no textual 
imports, so they work as before. With -J, they always recompile.