Don't trim quoted strings

When parsing condition expressions, if the type of an ast node is
String (aka quoted string), don't trim whitespace from the value. This
ensures that conditions that want to match exact strings e.g. command
lines with leading/trailing spaces will work properly.

This fixes #253.

userspace/engine/lua/parser.lua

@@ -130,7 +130,7 @@ end
 
 local function terminal (tag)
    -- Rather than trim the whitespace in this way, it would be nicer to exclude it from the capture...
-   return token(V(tag), tag) / function (tok) return { type = tag, value = trim(tok)} end
+   return token(V(tag), tag) / function (tok) val = tok; if tag ~= "String" then val = trim(tok) end; return { type = tag, value = val} end
 end
 
 local function unaryboolop (op, e)