Type conversion in GNU Radio Digital RF Source blocks

[ryanvolz]

When using one of the Digital RF Source blocks in GNU Radio Companion, it's easy to get errors due to mismatching types because the block has no way of knowing the data type when the flowgraph is constructed. It would be nice to let the user specify the type they want, so it can be enforced, and then handle the necessary type conversion internal to the block. This would save a lot of headaches when data is recorded as sc16 and you forget that and connect the source up to blocks that expect fc32.