Never throw an error when provider/clipboard.vim is sourced for the first time.
Save the error instead and expose it via `provider#clipboard#Error()`, mimicking
provider/python.vim.
This avoids the issue of nvim started daemons causing mountpoints to be
unmountable. This is currently the only place in runtime/ where this
calling convention occurred.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
xsel and xcopy may be available even if a valid X display is not. Also,
the availability of X may change at any time, so check on each
invocation.
Closes#1509.
Clipboard is implemented with platform-specific shell commands, and python is
implemented with the external plugin facility (rpc#* functions). The
script_host.py file(legacy python-vim emulation plugin) was moved/adapted from
the python client repository.
