Git.pm: config_boolean() -> config_bool()

This patch renames config_boolean() to config_bool() for consistency with
the commandline interface and because it is shorter but still obvious. ;-)
It also changes the return value from some obscure string to real Perl
boolean, allowing for clean user code.

Signed-off-by: Petr Baudis <pasky@suse.cz>
diff --git a/git-remote.perl b/git-remote.perl
index 52013fe..5763799 100755
--- a/git-remote.perl
+++ b/git-remote.perl
@@ -297,9 +297,9 @@
 	} elsif ($name eq 'default') {
 		undef @remotes;
 		for (sort keys %$remote) {
-			my $do_fetch = $git->config_boolean("remote." . $_ .
+			my $do_fetch = $git->config_bool("remote." . $_ .
 						    ".skipDefaultUpdate");
-			if (!defined($do_fetch) || $do_fetch ne "true") {
+			unless ($do_fetch) {
 				push @remotes, $_;
 			}
 		}