Use generic function to get sources

Currently, there is two different functions to determine pubkey’s amount for tx commands.

mentioned in issue #72 (closed)

assigned to @moul

added Doing label

unassigned @moul

removed Doing label

changed title from Use generic function to get pubkey amount to Use generic function to get sources

mentioned in commit ad953fbe

mentioned in commit cf586074

assigned to @moul

closed

removed D: Transfer label