Bug #1022

- Fixed bug #1022, where dependencies were note released when a blocking task
  was completed (thanks to Arkady Grudzinsky).
- The Task object now caches ::is_blocked and ::is_blocking Booleans that are
  determined on pending.data load.
- Simplified and sped up color rule processing using cached values, reducing
  the number of map lookups, and removed loop invariants when the rules are
  not defined.
- Simplified urgency calculations given the cached values for blocked/blocking.
- On load, pending.data is scanned for accurate blocked/blocking status
  determination.
- Obsoleted and removed complex single-task dependency calculations.
- Sped up 'nag' processing by using cached values..
- Modified the 'show' command to consider color.blocking to be valid.
- Added default config value for color.blocking, and included it in the
  precedence list ahead of blocked, as it is more important.
- Updated taskrc.5 man page to include the new color.blocking rule, and its
  place in the rule precedence.

src/Config.cpp

@@ -207,6 +207,7 @@ std::string Config::_defaults =
   "color.pri.L=rgb245                             # Color of priority:L tasks\n"
   "color.tagged=rgb031                            # Color of tagged tasks\n"
   "color.blocked=white on color8                  # Color of blocked tasks\n"
+  "color.blocking=white on color7                # Color of blocking tasks\n"
   "#color.completed=on blue                       # Color of completed tasks\n"
   "#color.deleted=on blue                         # Color of deleted tasks\n"
 #else
@@ -267,7 +268,7 @@ std::string Config::_defaults =
   "# Here is the rule precedence order, highest to lowest.\n"
   "# Note that these are just the color rule names, without the leading 'color.'\n"
   "#      and any trailing '.value'.\n"
-  "rule.precedence.color=due.today,active,blocked,overdue,due,scheduled,keyword.,project.,tag.,recurring,pri.,tagged,completed,deleted\n"
+  "rule.precedence.color=due.today,active,blocking,blocked,overdue,due,scheduled,keyword.,project.,tag.,recurring,pri.,tagged,completed,deleted\n"
   "\n"
   "# Shadow file support\n"
   "#shadow.file=/tmp/shadow.txt                   # Location of shadow file\n"