Support both decimal and hex values for uint dissectors.

And, while we're at it, reject entries with invalid numbers.

(Also clean up some indentation problems.)

Change-Id: I2ecc9605323eb462db5e508f7bd6d56ffc9adc0f
Reviewed-on: https://code.wireshark.org/review/3420
Reviewed-by: Guy Harris <guy@alum.mit.edu>