Change dependency policy

[jvegh]

It seems to me that presently using --use only adds an item to the 'DEPENDS' list, without any verification: BASIS accepts any name, and later attempts to configure and build that dependency. I suggest to compare that name against the names of internal modules, and accept --use without any message only in case of match. In addition, further compare should be made for name against known, but not implemented in BASIS, names, if found, with the warning, that the user must install the corresponding files in BASIS, and for the rest, flag the name as a probable mistype.
Presently, a mistyped name leads to error package not found, which is only true for case 3 above. A question asking did you mean "Xyz" when typed "xyz" would be very helpful. (consider FLEX, flex, Flex, gflags, Gflags, GFlags, etc.)