Hide dialogs for library clean/scan by default if automatically triggered.

This doesn't show dialogs and progress bars for library clean or scan if
initiated by an add-on or by a JSON-RPC client by default, as they're assumed
to be automatically triggered.

*library.backgroundupdate is still supported to let the user choose to not show
the progress even if user-initiated as it may take a while.
json-rpc: Add "showdialogs" to Audio/VideoLibrary.Clean/Scan. Bump to 6.19.0.
edit control: fix T9/SMS input for INPUT_TYPE_FILTER controls
changed: Log http error when Curl fillbuffer fails
[configure] always define USE_X11
Merge pull request #5514 from wsnipex/fix-feh

[configure] always define USE_X11
Merge pull request #5324 from anaconda/cleandb-background
Merge pull request #5512 from arnova/curl_errors

changed: Log http error when Curl fillbuffer fails
Merge pull request #5500 from Montellese/fix_edit_control_filter_sms_input
fixed: wrong label used when adjusting 'contrast' (closes #15483)
Merge pull request #5516 from mkortstiege/contrast_label

fixed: wrong label used when adjusting 'contrast' (closes #15483)
fixed: wrong label used when adjusting 'gamma'
[tests/darwin] - fixed g_sysinfo.GetManufacturerName() test on osx