Coccinelle: Update the documentation

 - The new default mode is 'report'.
 - The available modes are detailed a bit more.
 - Some information about the use of spatch options are
   also given concerning the use of indexing tools.
Signed-off-by: Nicolas Palix <nicolas.palix@imag.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Documentation/coccinelle.txt

@@ -48,7 +48,7 @@ A Coccinelle-specific target is defined in the top level
 Makefile. This target is named 'coccicheck' and calls the 'coccicheck'
 front-end in the 'scripts' directory.
 
-Four modes are defined: patch, report, context, and org. The mode to
+Four basic modes are defined: patch, report, context, and org. The mode to
 use is specified by setting the MODE variable with 'MODE=<mode>'.
 
 'patch' proposes a fix, when possible.
@@ -62,16 +62,22 @@ diff-like style.Lines of interest are indicated with '-'.
 'org' generates a report in the Org mode format of Emacs.
 
 Note that not all semantic patches implement all modes. For easy use
-of Coccinelle, the default mode is "chain" which tries the previous
-modes in the order above until one succeeds.
+of Coccinelle, the default mode is "report".
 
-To make a report for every semantic patch, run the following command:
+Two other modes provide some common combinations of these modes.
 
-	make coccicheck MODE=report
+'chain' tries the previous modes in the order above until one succeeds.
+
+'rep+ctxt' runs successively the report mode and the context mode.
+	   It should be used with the C option (described later)
+	   which checks the code on a file basis.
 
-NB: The 'report' mode is the default one.
+Examples:
+	To make a report for every semantic patch, run the following command:
+
+		make coccicheck MODE=report
 
-To produce patches, run:
+	To produce patches, run:
 
 		make coccicheck MODE=patch
 
@@ -129,26 +135,33 @@ To check only newly edited code, use the value 2 for the C flag, i.e.
 
     make C=2 CHECK="scripts/coccicheck"
 
+In these modes, which works on a file basis, there is no information
+about semantic patches displayed, and no commit message proposed.
+
 This runs every semantic patch in scripts/coccinelle by default. The
 COCCI variable may additionally be used to only apply a single
 semantic patch as shown in the previous section.
 
-The "chain" mode is the default. You can select another one with the
+The "report" mode is the default. You can select another one with the
 MODE variable explained above.
 
-In this mode, there is no information about semantic patches
-displayed, and no commit message proposed.
-
  Additional flags
 ~~~~~~~~~~~~~~~~~~
 
 Additional flags can be passed to spatch through the SPFLAGS
 variable.
 
-    make SPFLAGS=--use_glimpse coccicheck
+    make SPFLAGS=--use-glimpse coccicheck
+    make SPFLAGS=--use-idutils coccicheck
 
 See spatch --help to learn more about spatch options.
 
+Note that the '--use-glimpse' and '--use-idutils' options
+require external tools for indexing the code. None of them is
+thus active by default. However, by indexing the code with
+one of these tools, and according to the cocci file used,
+spatch could proceed the entire code base more quickly.
+
  Proposing new semantic patches
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~