post queries: support single-quoted strings in metatags.

app/logical/post_query/ast.rb

@@ -358,7 +358,7 @@ class PostQuery
       def quoted_value
         return nil unless metatag?
 
-        if value.include?(" ") || value.starts_with?('"') || value.empty?
+        if value.include?(" ") || value.starts_with?('"') || value.starts_with?("'") || value.empty?
           %Q{"#{value.gsub(/"/, '\\"')}"}
         else
           value

app/logical/post_query/parser.rb

@@ -24,6 +24,7 @@ require "strscan"
 # metatag       = metatag_name ":" quoted_string
 # metatag_name  = "user" | "fav" | "pool" | "order" | ...
 # quoted_string = '"' /[^"]+/ '"'
+#               | "'" /[^']+/ "'"
 # tag           = /[^ *]+/
 # wildcard      = /[^ ]+/
 #
@@ -172,6 +173,10 @@ class PostQuery
           a = accept(/([^"\\]|\\")*/).gsub(/\\"/, '"') # handle backslash escaped quotes
           expect('"')
           a
+        elsif accept("'")
+          a = accept(/([^'\\]|\\')*/).gsub(/\\'/, "'") # handle backslash escaped quotes
+          expect("'")
+          a
         else
           string(/[^ ]+/)
         end