Fixes this error, as seen when trying to open a guest VM when
virt-viewer is accessed over ssh with X forwarding:
GLib-GIO-ERROR **: Settings schema 'org.gnome.system.proxy' is not installed
A similar issue was fixed for virt-manager in commit
fb8a2b3be7f86481904636721f7fec99c30df389 ("virt-manager: fix missing
schema error")
* Add missing dependency on 'spice_protocol'
* Fix new build error which came now that ./configure enables SPICE support:
building virt-viewer
CCLD virt-viewer
/nix/store/b8qhjrwf8sf9ggkjxqqav7f1m6w83bh0-binutils-2.23.1/bin/ld: cannot find -lgdbm
/nix/store/b8qhjrwf8sf9ggkjxqqav7f1m6w83bh0-binutils-2.23.1/bin/ld: cannot find -lcap
collect2: error: ld returned 1 exit status
Fix by adding gddbm and libcap as inputs. Yes, libcap is needed
_in addition_ to libcap_ng (I tested removing libcap_ng, it failed).
Without this change, virt-viewer cannot be used with guests machines
that uses SPICE.
