JMAPSieve/sieve-test-extensive: Add more tests, and don't escape '\'

The escaping of '\' was surprising and problematic when doing other types of
tests, like inline jmapquery expressions.

Rather than using that, escape manually when needed.

cassandane/tiny-tests/JMAPSieve/sieve-test-extensive

@@ -2,15 +2,40 @@
 use Cassandane::Tiny;
 use Sub::Install;
 
+### basic variable support
+add_sieve_tests(
+    "variables_set_get",
+        'set "foo" "bar"; log "foo: ${foo}";',
+        [
+            [ 'log', {}, [ 'foo: bar' ] ],
+            [ 'keep', {}, [] ],
+        ],
+);
+
+### jmapquery
+add_sieve_tests(
+    "jmapquery_matches",
+        'if jmapquery "{\"from\" : \"sam\"}" {
+            fileinto "Matched";
+        }',
+        [ [ 'fileinto', {}, [ 'Matched' ] ] ],
+
+    "jmapquery_does_not_match",
+        'if jmapquery "{\"from\" : \"bugs\"}" {
+            fileinto "Matched";
+        }',
+        [ [ 'keep', {}, [] ] ],
+);
+
 ### fileinto
 add_sieve_tests(
     "fileinto_basic",
         'fileinto "foo";',
         [ ['fileinto', {}, [ 'foo' ] ] ],
 
     "fileinto_specialuse",
-        'fileinto :specialuse "\\junk" "Trash";',
-        [ ['fileinto', { specialuse => '\\junk' }, [ 'Trash' ] ] ],
+        'fileinto :specialuse "\\\\junk" "Trash";',
+        [ ['fileinto', { specialuse => '\junk' }, [ 'Trash' ] ] ],
 
     "fileinto_mailboxid",
         'fileinto :mailboxid "a-b-c-d" "Alphabet";',
@@ -44,6 +69,17 @@ add_sieve_tests(
         ],
 );
 
+### exists
+add_sieve_tests(
+    "exists",
+        'if exists ["From"] { fileinto "FromHeaderFound"; }',
+        [ ['fileinto', {}, [ 'FromHeaderFound' ] ] ],
+
+    "exists_not",
+        'if not exists ["From"] { fileinto "FromHeaderFound"; }',
+        [ ['keep', {}, [] ] ],
+);
+
 sub add_sieve_tests {
     my (@tests) = @_;
 
@@ -114,13 +150,12 @@ sub new_sieve_blob {
 
     xlog "create script";
     my $fullscript = <<EOF;
-require ["fileinto", "imap4flags", "copy", "variables", "mailbox", "mailboxid", "special-use"];
+require ["fileinto", "imap4flags", "copy", "variables", "mailbox", "mailboxid", "special-use", "vnd.cyrus.log", "vnd.cyrus.jmapquery"];
 
 $sieve
 EOF
 
     $fullscript =~ s/\r?\n/\r\n/gs;
-    $fullscript =~ s/\\/\\\\/gs;
 
     my $res = $jmap->CallMethods([
         ['Blob/upload', {