allow input methods to be enabled

[Antoine Martin]

Currently, the server will try to disable all input methods to try avoid problems by setting the following environment variables:

DISABLE_IMSETTINGS=true
GTK_IM_MODULE=xim
QT_IM_MODULE=xim
IMSETTINGS_MODULE=none
XMODIFIERS=""

But some users (see ​this ML discussion) may want to enable input methods without knowing about all those values.
For example for ibus:

GTK_IM_MODULE=ibus
QT_IM_MODULE=ibus
XMODIFIERS="@im=ibus"

We should provide a better way of enabling this.

We need to:

• figure out what normally sets those values (a session script somewhere?)
• does any of it need dbus or other dependencies?
• does it interfere when running multiple sessions
• what is the best config / command-line switch? (input-methods=[none|ibus|...)

[Antoine Martin]

Done in r7272.

Adds the input-method switch. Options:

• none

Disable input methods completely and prevent it from interfering with keyboard input. This is the default.

• keep

Keeps the environment unchanged. You are responsible for ensuring it is correct.

• xim

Enables the ​X Input Method.

• IBus

Enables the ​Intelligent Input Bus.
.IP \fBSCIM\fP
Enables the ​Smart Common Input Method.
.IP \fBuim\fP
Enables the ​Universal Input Method.

[Antoine Martin]

Was done for milestone 0.14

[Antoine Martin]

See also: ​GTK apps do not integrate with the Windows input..

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/634