Merge branch 'jk/gpg-interface-cleanup'

A new run-command API function pipe_command() is introduced to sanely feed data to the standard input while capturing data from the standard output and the standard error of an external process, which is cumbersome to hand-roll correctly without deadlocking. The codepath to sign data in a prepared buffer with GPG has been updated to use this API to read from the status-fd to check for errors (instead of relying on GPG's exit status). * jk/gpg-interface-cleanup: gpg-interface: check gpg signature creation status sign_buffer: use pipe_command verify_signed_buffer: use pipe_command run-command: add pipe_command helper verify_signed_buffer: use tempfile object verify_signed_buffer: drop pbuf variable gpg-interface: use child_process.args