Fix prompt for commands over SSH

When executing commands over SSH, such as SCP, the server (tput)
complains that there is no terminal defined. This fix sets the T_*
variables only if the TERM variable is not empty.

bash/bashrc.common

@@ -7,10 +7,20 @@ add_to_path() {
 }
 
 # Define the colors used by the prompt
+if [[ ! -z $TERM && "$TERM" != "dumb" ]]
+then
     T_B=$(tput setaf 4) # Blue
     T_G=$(tput setaf 2) # Green
     T_Y=$(tput setaf 3) # Yellow
     T_S=$(tput sgr0)    # Reset
+else
+    # We've probably been invoked by an SSH command, there's no terminal
+    # to deal with. Don't bother coloring the prompt.
+    T_B=''
+    T_G=''
+    T_Y=''
+    T_S=''
+fi
 
 # Import the Git prompt shell functions. These can be found
 # @github:git/git/contrib/completion/git_prompt.sh