Export `setRowLower` etc. in the C interface

[mtanneau]

I'm working with Clp through its Julia API, which uses Clp's C interface.

I'm trying to change the bounds on one constraint at a time, which is possible in Clp's C++ interface (see setRowLower, setRowUpper and SetRowBounds), but not in its C interface.

Only chrRowLower and chrRowUpper seem to be exported there.

Is there any technical reason for not exporting this?

Happy to PR.