Accept a trailing space at end of PEM lines

With certs being copy-pasted from webmails and all, this will probably become
more and more common.
diff --git a/ChangeLog b/ChangeLog
index b4bed6c..a80a85e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,7 @@
 Changes
    * Add SSL_MIN_DHM_BYTES configuration parameter in config.h to choose the
      minimum size of Diffie-Hellman parameters accepted by the client.
+   * The PEM parser now accepts a trailing space at end of lines (#226).
 
 = Version 1.2.14 released 2015-06-26
 
diff --git a/library/pem.c b/library/pem.c
index 4f853b5..5c973ac 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -208,12 +208,14 @@
         return( POLARSSL_ERR_PEM_NO_HEADER_FOOTER_PRESENT );
 
     s1 += strlen( header );
+    if( *s1 == ' '  ) s1++;
     if( *s1 == '\r' ) s1++;
     if( *s1 == '\n' ) s1++;
     else return( POLARSSL_ERR_PEM_NO_HEADER_FOOTER_PRESENT );
 
     end = s2;
     end += strlen( footer );
+    if( *end == ' '  ) end++;
     if( *end == '\r' ) end++;
     if( *end == '\n' ) end++;
     *use_len = end - data;