Primary key ist not selected properly using bash+GPG+curl

I've tried proving a few things using the bash/GPG/curl option. But the generated script would _not_ use my primary GPG key for signing but a signing subkey (S, not C!) I have in my keyring too. In this case a simple

```
gpg -u "$MASTERKEYID" --sign
```

will silently select the _subkey_ for signing. In order to really force the primary key this command will do by adding an `!` to the id:

```
gpg -u "$MASTERKEYID!" --sign
```

Search the generated bash/GPG/curl script for the use of MASTERKEYID and inspect how the signing command selects a key. Confirm the behavior with a keyring containing a primary key and signing subkey, then verify that signing explicitly targets the primary key.

Written by the indexing model from the issue text.