gitweb: Skip 'modification times' tests when no date parser available

The If-Modified-Since support in Gitweb is conditional on the
availability of a date parser from either the HTTP::Date or
Time::ParseDate modules. If a suitable parser is not available,
then the corresponding 'modification times' tests should be skipped.

Introduce the DATE_PARSER test prerequisite and use it to skip
all of the dependent tests.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9501-gitweb-standalone-http-status.sh

@@ -12,6 +12,13 @@ code and message.'
 
 . ./gitweb-lib.sh
 
+#
+# Gitweb only provides the functionality tested by the 'modification times'
+# tests if it can access a date parser from one of these modules:
+#
+perl -MHTTP::Date -e 0 >/dev/null 2>&1 && test_set_prereq DATE_PARSER
+perl -MTime::ParseDate -e 0 >/dev/null 2>&1 && test_set_prereq DATE_PARSER
+
 # ----------------------------------------------------------------------
 # snapshot settings
 
@@ -115,53 +122,53 @@ test_debug 'cat gitweb.output'
 # ----------------------------------------------------------------------
 # modification times (Last-Modified and If-Modified-Since)
 
-test_expect_success 'modification: feed last-modified' '
+test_expect_success DATE_PARSER 'modification: feed last-modified' '
 	gitweb_run "p=.git;a=atom;h=master" &&
 	grep "Status: 200 OK" gitweb.headers &&
 	grep "Last-modified: Thu, 7 Apr 2005 22:14:13 +0000" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: feed if-modified-since (modified)' '
+test_expect_success DATE_PARSER 'modification: feed if-modified-since (modified)' '
 	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
 	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
 	gitweb_run "p=.git;a=atom;h=master" &&
 	grep "Status: 200 OK" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: feed if-modified-since (unmodified)' '
+test_expect_success DATE_PARSER 'modification: feed if-modified-since (unmodified)' '
 	export HTTP_IF_MODIFIED_SINCE="Thu, 7 Apr 2005 22:14:13 +0000" &&
 	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
 	gitweb_run "p=.git;a=atom;h=master" &&
 	grep "Status: 304 Not Modified" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: snapshot last-modified' '
+test_expect_success DATE_PARSER 'modification: snapshot last-modified' '
 	gitweb_run "p=.git;a=snapshot;h=master;sf=tgz" &&
 	grep "Status: 200 OK" gitweb.headers &&
 	grep "Last-modified: Thu, 7 Apr 2005 22:14:13 +0000" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: snapshot if-modified-since (modified)' '
+test_expect_success DATE_PARSER 'modification: snapshot if-modified-since (modified)' '
 	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
 	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
 	gitweb_run "p=.git;a=snapshot;h=master;sf=tgz" &&
 	grep "Status: 200 OK" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: snapshot if-modified-since (unmodified)' '
+test_expect_success DATE_PARSER 'modification: snapshot if-modified-since (unmodified)' '
 	export HTTP_IF_MODIFIED_SINCE="Thu, 7 Apr 2005 22:14:13 +0000" &&
 	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
 	gitweb_run "p=.git;a=snapshot;h=master;sf=tgz" &&
 	grep "Status: 304 Not Modified" gitweb.headers
 '
 test_debug 'cat gitweb.headers'
 
-test_expect_success 'modification: tree snapshot' '
+test_expect_success DATE_PARSER 'modification: tree snapshot' '
 	ID=`git rev-parse --verify HEAD^{tree}` &&
 	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
 	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&