www: add configurable limiters

Currently only for git-http-backend use, this allows limiting
the number of spawned processes per-inbox or by group, if there
are multiple large inboxes amidst a sea of small ones.

For example, a "big" repo limiter could be used for big inboxes:
which would be shared between multiple repos:

[limiter "big"]
	max = 4
[publicinbox "git"]
	address = git@vger.kernel.org
	mainrepo = /path/to/git.git
	; shared limiter with giant:
	httpbackendmax = big
[publicinbox "giant"]
	address = giant@project.org
	mainrepo = /path/to/giant.git
	; shared limiter with git:
	httpbackendmax = big

; This is a tiny inbox, use the default limiter with 32 slots:
[publicinbox "meta"]
	address = meta@public-inbox.org
	mainrepo = /path/to/meta.git

1 files changed, 2 insertions, 0 deletions

diff --git a/t/config.t b/t/config.t
index dc448cdf..77e8f4ac 100644
--- a/t/config.t
+++ b/t/config.t
@@ -30,6 +30,7 @@ my $tmpdir = tempdir('pi-config-XXXXXX', TMPDIR => 1, CLEANUP => 1);
                 'url' => 'http://example.com/meta',
                 -primary_address => 'meta@public-inbox.org',
                 'name' => 'meta',
+                -pi_config => $cfg,
         }, "lookup matches expected output");
 
         is($cfg->lookup('blah@example.com'), undef,
@@ -45,6 +46,7 @@ my $tmpdir = tempdir('pi-config-XXXXXX', TMPDIR => 1, CLEANUP => 1);
                 'domain' => 'public-inbox.org',
                 'name' => 'test',
                 'url' => 'http://example.com/test',
+                -pi_config => $cfg,
         }, "lookup matches expected output for test");
 }