Fixed help of Diff and ShowCommands commands

jgit.sh <command> --help was not working for the commands Diff
and ShowCommands because of missing metaVar information. Missing
information is added here.

Change-Id: I0ab7e35006b6aa7d4326a634309dddfcdb78f2a6
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>

org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/CLIText.properties

@@ -61,10 +61,12 @@ metaVar_author=AUTHOR
 metaVar_base=base
 metaVar_bucket=BUCKET
 metaVar_command=command
+metaVar_commandDetail=DETAIL
 metaVar_commitOrTag=COMMIT|TAG
 metaVar_commitish=commit-ish
 metaVar_configFile=FILE
 metaVar_connProp=conn.prop
+metaVar_diffAlg=ALGORITHM
 metaVar_directory=DIRECTORY
 metaVar_file=FILE
 metaVar_filepattern=filepattern
@@ -149,7 +151,7 @@ usage_configureTheServiceInDaemonServicename=configure the service in daemon.ser
 usage_deleteBranchEvenIfNotMerged=delete branch (even if not merged)
 usage_deleteFullyMergedBranch=delete fully merged branch
 usage_detectRenames=detect renamed files
-usage_diffAlgorithm=the diff algorithm to use
+usage_diffAlgorithm=the diff algorithm to use. Currently supported are: 'myers', 'histogram'
 usage_directoriesToExport=directories to export
 usage_disableTheServiceInAllRepositories=disable the service in all repositories
 usage_displayAListOfAllRegisteredJgitCommands=Display a list of all registered jgit commands

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Diff.java

@@ -111,7 +111,7 @@ class Diff extends TextBuiltin {
 		}
 	};
 
-	@Option(name = "--algorithm", usage = "usage_diffAlgorithm")
+	@Option(name = "--algorithm", metaVar = "metaVar_diffAlg", usage = "usage_diffAlgorithm")
 	void setAlgorithm(SupportedAlgorithm s) {
 		diffFmt.setDiffAlgorithm(s.algorithm);
 	}

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/ShowCommands.java

@@ -54,7 +54,7 @@ import org.eclipse.jgit.pgm.TextBuiltin;
 
 @Command(usage = "usage_displayAListOfAllRegisteredJgitCommands")
 class ShowCommands extends TextBuiltin {
-	@Option(name = "--pretty", usage = "usage_alterTheDetailShown")
+	@Option(name = "--pretty", metaVar = "metaVar_commandDetail", usage = "usage_alterTheDetailShown")
 	private Format pretty = Format.USAGE;
 
 	@Override