Make powerline.vim work in compatible mode

powerline/bindings/vim/plugin/powerline.vim

@@ -3,39 +3,41 @@ if exists('g:powerline_loaded')
 endif
 let g:powerline_loaded = 1
 
-function! s:CriticalError(message)
-	echohl ErrorMsg
-	echomsg a:message
-	echohl None
-endfunction
-
 if ! has('python') && ! has('python3')
 	if !exists('g:powerline_no_python_error')
-		call s:CriticalError('You need vim compiled with Python 2.6+ or 3.2+ support
+		echohl ErrorMsg
-			\ for Powerline to work. Please consult the documentation for more details.')
+			echom 'You need vim compiled with Python 2.6, 2.7 or 3.2 and later support'
+			echom 'for Powerline to work. Please consult the documentation for more'
+			echom 'details.'
+		echohl None
 	endif
 	finish
 endif
 
-let s:pycmd = substitute(get(g:, 'powerline_pycmd', has('python') ? 'py' : 'py3'),
+let s:pycmd = substitute(get(g:, 'powerline_pycmd', has('python') ? 'py' : 'py3'), '\v^(py)%[thon](3?)$', '\1\2', '')
-			\'\v^(py)%[thon](3?)$', '\1\2', '')
 let s:pyeval = get(g:, 'powerline_pyeval', s:pycmd.'eval')
 
 let s:import_cmd = 'from powerline.vim import setup as powerline_setup'
 try
-	execute s:pycmd "try:\n"
+	let s:pystr  = "try:\n"
-				\  ."	".s:import_cmd."\n"
+	let s:pystr .= "	".s:import_cmd."\n"
-				\  ."except ImportError:\n"
+	let s:pystr .= "except ImportError:\n"
-				\  ."	import sys, vim\n"
+	let s:pystr .= "	import sys, vim\n"
-				\  ."	sys.path.append(vim.eval('expand(\"<sfile>:h:h:h:h:h\")'))\n"
+	let s:pystr .= "	sys.path.append(vim.eval('expand(\"<sfile>:h:h:h:h:h\")'))\n"
-				\  ."	".s:import_cmd
+	let s:pystr .= "	".s:import_cmd."\n"
+	execute s:pycmd s:pystr
+	unlet s:pystr
 	let s:launched = 1
 finally
 	if !exists('s:launched')
-		call s:CriticalError('An error occurred while importing the Powerline package.
+		echohl ErrorMsg
-			\ This could be caused by an invalid sys.path setting, or by an incompatible
+			echom 'An error occurred while importing powerline package.'
-			\ Python version (Powerline requires Python 2.6+ or 3.2+ to work). Please consult
+			echom 'This could be caused by invalid sys.path setting,'
-			\ the troubleshooting section in the documentation for possible solutions.')
+			echom 'or by an incompatible Python version (powerline requires'
+			echom 'Python 2.6, 2.7 or 3.2 and later to work). Please consult'
+			echom 'the troubleshooting section in the documentation for'
+			echom 'possible solutions.'
+		echohl None
 		finish
 	else
 		unlet s:launched