do not unset @tpm-install, @tpm-update, @tpm-clean and @plugin variables after tpm has launched, fixes #531

.tmux.conf

@@ -1374,11 +1374,13 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 #       tmux display "GitHub doesn't seem to be reachable, skipping installing and/or updating tpm and plugins..."
 #     fi
 #
-#     [ -z "$(tmux show -gv '@tpm-install')" ] && tmux set -g '@tpm-install' 'I'
-#     [ -z "$(tmux show -gv '@tpm-update')" ] && tmux set -g '@tpm-update' 'u'
-#     [ -z "$(tmux show -gv '@tpm-clean')" ] && tmux set -g '@tpm-clean' 'M-u'
+#     [ -z "$(tmux show -gqv '@tpm-install')" ] && tmux set -g '@tpm-install' 'I'
+#     [ -z "$(tmux show -gqv '@tpm-update')" ] && tmux set -g '@tpm-update' 'u'
+#     [ -z "$(tmux show -gqv '@tpm-clean')" ] && tmux set -g '@tpm-clean' 'M-u'
 #     [ -f "$TMUX_PLUGIN_MANAGER_PATH/tpm/tpm" ] && "$TMUX_PLUGIN_MANAGER_PATH/tpm/tpm"
-#     tmux set -gu '@tpm-install' \; set -gu '@tpm-update' \; set -gu '@tpm-clean' \; set -gu '@plugin'
+#     if [ $_tmux_version -gt 260 ]; then
+#       tmux set -gu '@tpm-install' \; set -gu '@tpm-update' \; set -gu '@tpm-clean' \; set -gu '@plugin'
+#     fi
 #   fi
 #
 #   if [ -z "$window_active" ] && [ $_tmux_version -lt 240 ]; then