Merge branch 'bt/gpg-interface'

Merge branch 'bt/gpg-interface'

What is queued here is only the obviously correct and
uncontroversial code clean-up part, which is an earlier 7 patches,
of a larger series.

The remainder that is not queued introduces a few configuration
variables to deal with e-signature backends with different
signature format.

* bt/gpg-interface:
  gpg-interface: find the last gpg signature line
  gpg-interface: extract gpg line matching helper
  gpg-interface: fix const-correctness of "eol" pointer
  gpg-interface: use size_t for signature buffer size
  gpg-interface: modernize function declarations
  gpg-interface: handle bool user.signingkey
  t7004: fix mistaken tag name