Log Message:
mate-session-manager: update to 1.26.0

Change log:

### mate-session-manager 1.26.0

  * Translations update
  * update copyright to 2021
  * Follow freedesktop guidelines to disable autorun using Hidden key
  * capplet: use a function to set the visibility of treeview rows
  * Look for the location of the locking screen app using user's PATH
  * capplet: memory leak
  * Fix building Serbian translation
  * mate-session-check-accelerated-common: missing include guard
  * capplet: i18n parameter_string argument of gtk_init_with_args
  * build: allow users to disable gettext support (--disable-nls)
  * build: set GETTEXT_PACKAGE=AC_PACKAGE_NAME
  * Support xscreensaver when mate-screensaver is not available
  * Remove warning -Wshadow
  * Remove USE_MATE2_MACROS from autogen.sh (legacy)

### mate-session-manager 1.25.0

  * Build: disable Serbian translations to fix building
  * Translations update
  * Change some icons by other always available
  * gsm-properties-dialog: Refactor notebook scroll event
  * Update compilation instructions
  * Using #include with system libraries
  * use libegg submodule
  * Add git.mk to generate .gitignore
  * Add tab scrolling support for GTK3
  * build: silent build warnings for distcheck
  * Accept Desktop Entry Specification v1.1
  * build: do not override the default value for MATE_COMPILE_WARNINGS
  * build: make libglesv2 optional