Bug#814676: vinagre 3.20.0 requires freerdp_get_last_error

[Anders Jonsson]

Another program that now needs a newer version of freeRDP is Vinagre
3.20 that needs
freerdp_get_last_error to compile.

freerdp_get_last_error was added in
https://github.com/FreeRDP/FreeRDP/commit/d1b9565f515597df421226aca38bffeca5c3fdb1