Move commit reencoding parameter parsing to revision.c

This way, git-rev-list and git-diff-tree with --pretty can use
it.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -21,6 +21,7 @@ SYNOPSIS
 	     [ \--stdin ]
 	     [ \--topo-order ]
 	     [ \--parents ]
+	     [ \--encoding[=<encoding>] ]
 	     [ \--(author|committer|grep)=<pattern> ]
 	     [ [\--objects | \--objects-edge] [ \--unpacked ] ]
 	     [ \--pretty | \--header ]

Documentation/pretty-formats.txt

@@ -76,3 +76,10 @@ displayed in full, regardless of whether --abbrev or
 --no-abbrev are used, and 'parents' information show the
 true parent commits, without taking grafts nor history
 simplification into account.
+
+--encoding[=<encoding>]::
+	The commit objects record the encoding used for the log message
+	in their encoding header; this option can be used to tell the
+	command to re-code the commit log message in the encoding
+	preferred by the user.  For non plumbing commands this
+	defaults to UTF-8.

revision.c

@@ -1039,6 +1039,14 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 				all_match = 1;
 				continue;
 			}
+			if (!strncmp(arg, "--encoding=", 11)) {
+				arg += 11;
+				if (strcmp(arg, "none"))
+					git_log_output_encoding = strdup(arg);
+				else
+					git_log_output_encoding = "";
+				continue;
+			}
 
 			opts = diff_opt_parse(&revs->diffopt, argv+i, argc-i);
 			if (opts > 0) {