git-check-attr: Add an --all option to show all attributes

Add new usage patterns

    git check-attr [-a | --all] [--] pathname...
    git check-attr --stdin [-a | --all] < <list-of-paths>

which display all attributes associated with the specified file(s).

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-check-attr.txt b/Documentation/git-check-attr.txt
index 30eca6c..798e5d5 100644
--- a/Documentation/git-check-attr.txt
+++ b/Documentation/git-check-attr.txt
@@ -9,8 +9,8 @@
 SYNOPSIS
 --------
 [verse]
-'git check-attr' attr... [--] pathname...
-'git check-attr' --stdin [-z] attr... < <list-of-paths>
+'git check-attr' [-a | --all | attr...] [--] pathname...
+'git check-attr' --stdin [-z] [-a | --all | attr...] < <list-of-paths>
 
 DESCRIPTION
 -----------
@@ -19,6 +19,11 @@
 
 OPTIONS
 -------
+-a, --all::
+	List all attributes that are associated with the specified
+	paths.  If this option is used, then 'unspecified' attributes
+	will not be included in the output.
+
 --stdin::
 	Read file names from stdin instead of from the command-line.
 
@@ -69,6 +74,13 @@
 org/example/MyClass.java: myAttr: set
 ---------------
 
+* Listing all attributes for a file:
+---------------
+$ git check-attr --all -- org/example/MyClass.java
+org/example/MyClass.java: diff: java
+org/example/MyClass.java: myAttr: set
+---------------
+
 * Listing an attribute for multiple files:
 ---------------
 $ git check-attr myAttr -- org/example/MyClass.java org/example/NoMyAttr.java