Merge branch 'xx/remote-server-option-config'

Merge branch 'xx/remote-server-option-config'

A new configuration variable remote.<name>.serverOption makes the
transport layer act as if the --serverOption=<value> option is
given from the command line.

* xx/remote-server-option-config:
  ls-remote: leakfix for not clearing server_options
  fetch: respect --server-option when fetching multiple remotes
  transport.c::handshake: make use of server options from remote
  remote: introduce remote.<name>.serverOption configuration
  transport: introduce parse_transport_option() method