Add support for context symbol in bashum ($BASHUM_CTXSYM)

If BASHUM_CTXSYM is set, show it in a different color.  This is intended
for special-purpose Bash invocations with modified environment, for example
when authentication to some remote service has been pre-set.

dotfiles/bash/colors.bashrc

 #!/bin/bash
 
+#
+# Context symbol used in title and prompt
+#
+BASHUM_CTXSYM=${BASHUM_CTXSYM:-}
+
 # get some fancy colorz
 BASHUM_COLOR_BLACK=$'\033[0;30m'
 BASHUM_COLOR_RED=$'\033[0;31m'

dotfiles/bash/post.bashrc

     echo -n "$BASHUM_PS_COLOR_LWHITE@"         # nice shiny at sign
     echo -n "$(__bashum__mkps1host)"        # hostname colored per host
     echo -n "$BASHUM_PS_COLOR_LYELLOW"         #\
+    test -n "$BASHUM_CTXSYM" \
+     && echo -n "[$BASHUM_CTXSYM]"             # > bashum's context symbol
     echo -n     '$(__bashum__task_context)' # > taskwarrior's context
     echo -n "$BASHUM_PS_COLOR_NORMAL"          #/
     echo -n "$BASHUM_PS_COLOR_LWHITE:"         # nice shiny colon
 
 __bashum__mkicon() {
     case "$SSH_CONNECTION" in
-        "") echo  ;;
-        *)  echo  ;;
+        "") echo -n  ;;
+        *)  echo -n  ;;
     esac
+    test -n "$BASHUM_CTXSYM" \
+     && echo " [$BASHUM_CTXSYM]"
 }
 
 __bashum__mkhostid() {