git-clone: Sync documentation to usage note.

Documentation advertises the new `--depth <n>' parameter with an equal
sign, while the usage notes (shown after `git-clone --help') do not.  If I
understood git-clone's source code correctly, the version without the
equal sign is correct, which is why this patch syncs documentation to the
usage note.

Signed-off-by: Christian Schlotter <schlotter@users.sourceforge.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/RelNotes-1.5.0.txt

@@ -448,7 +448,7 @@ Updates in v1.5.0 since v1.4.4 series
  - There is a partial support for 'shallow' repositories that
    keeps only recent history.  A 'shallow clone' is created by
    specifying how deep that truncated history should be
-   (e.g. "git clone --depth=5 git://some.where/repo.git").
+   (e.g. "git clone --depth 5 git://some.where/repo.git").
 
    Currently a shallow repository has number of limitations:
 

Documentation/git-clone.txt

@@ -11,7 +11,7 @@ SYNOPSIS
 [verse]
 'git-clone' [--template=<template_directory>] [-l [-s]] [-q] [-n] [--bare]
 	  [-o <name>] [-u <upload-pack>] [--reference <repository>]
-	  [--depth=<depth>] <repository> [<directory>]
+	  [--depth <depth>] <repository> [<directory>]
 
 DESCRIPTION
 -----------
@@ -96,7 +96,7 @@ OPTIONS
 	if unset the templates are taken from the installation
 	defined default, typically `/usr/share/git-core/templates`.
 
---depth=<depth>::
+--depth <depth>::
 	Create a 'shallow' clone with a history truncated to the
 	specified number of revs.  A shallow repository has
 	number of limitations (you cannot clone or fetch from