Show a clear error message if vim was compiled without Python, or wit…

…h a version of Python older than 2.5.

pyflakes.vim

@@ -22,11 +22,21 @@ if !exists('g:pyflakes_builtins')
 endif
 
 if !exists("b:did_python_init")
+    let b:did_python_init = 0
+
+    if !has('python')
+        echoerr "Error: the pyflakes.vim plugin requires Vim to be compiled with +python"
+        finish
+    endif
+
     python << EOF
 import vim
 import os.path
 import sys
 
+if sys.version_info[:2] < (2, 5):
+    raise AssertionError('Vim must be compiled with Python 2.5 or higher; you have ' + sys.version)
+
 # get the directory this script is in: the pyflakes python module should be installed there.
 scriptdir = os.path.join(os.path.dirname(vim.eval('expand("<sfile>")')), 'pyflakes')
 sys.path.insert(0, scriptdir)
@@ -86,6 +96,10 @@ EOF
     let b:did_python_init = 1
 endif
 
+if !b:did_python_init
+    finish
+endif
+
 au BufLeave <buffer> call s:ClearPyflakes()
 
 au BufEnter <buffer> call s:RunPyflakes()