Corrected various spelling mistakes (most of them reported by codespell).

INSTALL

···
  	For the real fix, applying Sun patches # 105490-05 (linker
 	patch) and # 105210-17 (libc and malloc patch) from
 	sunsolve.sun.com has been reported to stop these problems
-	from occuring.
+	from occurring.
 
 Linux
 

README.SECURITY

···
 
 - Backticks are handled specially when preparing % expandos for
   mailcap entries.  This fix will keep the current problem from
-  occuring, but we are sure there are other possible mailcap entries
+  occurring, but we are sure there are other possible mailcap entries
   where this doesn't help.
 
 - We have added a configuration variable named $mailcap_sanitize,

README.SSL

···
     openssl s_client -host <imap server> -port <port> -verify -debug -no_ssl2
     openssl s_client -host <imap server> -port <port> -verify -debug -no_ssl3
 
-You can also combine the options until you get a successfull connect.  Once
+You can also combine the options until you get a successful connect.  Once
 you know which options do not work, you can set the variables for non-working
 protocols to know.  The variables for the protocols are ssl_use_tlsv1, 
 ssl_use_sslv2, and ssl_use_sslv3.

TODO

···
   Note: This still requires some thought, since we'd have to store
   per-entry data in the menu structure.  As an alternative, we could
   extend the tag method to do something to more general flags. The
-  latter approach would make the implementation of propper
+  latter approach would make the implementation of proper
   tag-prefix behaviour more simple: Functions should only be applied
   when a message is tagged and visible.  Additionally, we must not
   access a menu's max field directly any more: Adding an entry to a

configure.ac

···
 ])
  
 if test x$have_smime != xno ; then
-	AC_DEFINE(CRYPT_BACKEND_CLASSIC_SMIME, 1, [Define if you want clasic S/MIME support.])
+	AC_DEFINE(CRYPT_BACKEND_CLASSIC_SMIME, 1, [Define if you want classic S/MIME support.])
 	MUTT_LIB_OBJECTS="$MUTT_LIB_OBJECTS smime.o crypt-mod-smime-classic.o"
 	SMIMEAUX_TARGET="smime_keys"
 fi

curs_lib.c

···
 
 /*
  * mutt_strwidth is like mutt_strlen except that it returns the width
- * refering to the number of characters cells.
+ * referring to the number of character cells.
  */
 
 int mutt_strwidth (const char *s)

help.c

···
   fputs (t1, f);
 
   /* don't try to press string into one line with less than 40 characters.
-     The double paranthesis avoid a gcc warning, sigh ... */
+     The double parenthesis avoids a gcc warning, sigh ... */
   if ((split = COLS < 40))
   {
     col_a = col = 0;

imap/message.c

···
    * IMAP server doesn't know the message has been \Seen. So we capture
    * the server's notion of 'read' and if it differs from the message info
    * picked up in mutt_read_rfc822_header, we mark the message (and context
-   * changed). Another possiblity: ignore Status on IMAP?*/
+   * changed). Another possibility: ignore Status on IMAP?*/
   read = h->read;
   newenv = mutt_read_rfc822_header (msg->fp, h, 0, 0);
   mutt_merge_envelopes(h->env, &newenv);

lib.c

···
 
 /*
  * Write the concatened pathname (dir + "/" + fname) into dst.
- * The slash is ommitted when dir or fname is of 0 length.
+ * The slash is omitted when dir or fname is of 0 length.
  * Returns NULL on error or a pointer to dst otherwise.
  */
 char *mutt_concatn_path (char *dst, size_t dstlen,

mh.c

···
      * number.  Mutt does _not_ behave like this.
      * 
      * Anyway, if this fails, the message is in the folder, so
-     * all what happens is that a concurrently runnung mutt will
+     * all what happens is that a concurrently running mutt will
      * lose flag modifications.
      */