Allow users to customize Ctrl-P's statusline

This lets you disable focus, prev, next:
	let g:Powerline#Segments#ctrlp#segments#focus = ''
	let g:Powerline#Segments#ctrlp#segments#prev = ''
	let g:Powerline#Segments#ctrlp#segments#next = ''

Closes Lokaltog#185.

autoload/Powerline/Segments/ctrlp.vim

@@ -1,9 +1,19 @@
+if !exists("g:Powerline#Segments#ctrlp#segments#focus ")
+	let g:Powerline#Segments#ctrlp#segments#focus = '%{"%0"}'
+endif
+if !exists("g:Powerline#Segments#ctrlp#segments#prev ")
+	let g:Powerline#Segments#ctrlp#segments#prev = '%-3{"%3"}'
+endif
+if !exists("g:Powerline#Segments#ctrlp#segments#next ")
+	let g:Powerline#Segments#ctrlp#segments#next = '%-3{"%5"}'
+endif
+
 let g:Powerline#Segments#ctrlp#segments = Pl#Segment#Init(['ctrlp'
-	\ , Pl#Segment#Create('focus', '%{"%0"}')
+	\ , Pl#Segment#Create('focus', g:Powerline#Segments#ctrlp#segments#focus)
 	\ , Pl#Segment#Create('byfname', '%{"%1"}')
-	\ , Pl#Segment#Create('prev', '%-3{"%3"}')
+	\ , Pl#Segment#Create('prev', g:Powerline#Segments#ctrlp#segments#prev)
 	\ , Pl#Segment#Create('item', '%-9{"%4"}')
-	\ , Pl#Segment#Create('next', '%-3{"%5"}')
+	\ , Pl#Segment#Create('next', g:Powerline#Segments#ctrlp#segments#next)
 	\ , Pl#Segment#Create('marked', '%{"%6" == " <+>" ? "" : strpart("%6", 2, len("%6") - 3)}')
 	\
 	\ , Pl#Segment#Create('count', '%-6{"%0"}')