Fix checks for battery plugin

These now check for the presence of the required function instead of
checking for the battery file in the enabled directory.

themes/base.theme.bash

@@ -474,13 +474,15 @@ function battery_char {
     fi
 }
 
-if [ ! -e "$BASH_IT"/plugins/enabled/battery.plugin.bash ]; then
+if ! command_exists battery_charge ; then
     # if user has installed battery plugin, skip this...
     function battery_charge (){
 	# no op
 	echo -n
     }
+fi
 
+if ! command_exists battery_char ; then
     function battery_char (){
 	# no op
 	echo -n

themes/brainy/brainy.theme.bash

@@ -152,7 +152,7 @@ ___brainy_prompt_clock() {
 }
 
 ___brainy_prompt_battery() {
-	[ ! -e $BASH_IT/plugins/enabled/battery.plugin.bash ] ||
+	! command_exists battery_percentage ||
 	[ "${THEME_SHOW_BATTERY}" != "true" ] && return
 	info=$(battery_percentage)
 	color=$bold_green

themes/demula/demula.theme.bash

@@ -84,7 +84,7 @@ ${D_BRANCH_COLOR}%b %r ${D_CHANGES_COLOR}%m%u ${D_DEFAULT_COLOR}"
 
 # checks if the plugin is installed before calling battery_charge
 safe_battery_charge() {
-  if [ -e "${BASH_IT}/plugins/enabled/battery.plugin.bash" ];
+  if command_exists battery_charge ;
   then
     battery_charge
   fi
@@ -127,4 +127,3 @@ ${D_INTERMEDIATE_COLOR}$ ${D_DEFAULT_COLOR}"
 
 # Runs prompt (this bypasses bash_it $PROMPT setting)
 safe_append_prompt_command prompt
-

themes/rana/rana.theme.bash

@@ -117,7 +117,7 @@ ${D_BRANCH_COLOR}%b %r ${D_CHANGES_COLOR}%m%u ${D_DEFAULT_COLOR}"
 
 # checks if the plugin is installed before calling battery_charge
 safe_battery_charge() {
-  if [ -e "${BASH_IT}/plugins/enabled/battery.plugin.bash" ];
+  if command_exists battery_charge ;
   then
     battery_charge
   fi