Enhancement - special tags

- Implemented the 'nocal' special tag.

ChangeLog

@@ -15,7 +15,8 @@
  + Improved man pages (thanks to Andy Lester).
  + Default .taskrc files are now largely empty, and rely almost completed
    on default values.
- + Special tags are now documented, and the 'tags' command highlights them.
+ + Special tags 'nocal', 'nocolor' and 'nonag' are implemented.
+ + The 'tags' command highlights special tags.
  + Fixed bug #427, preventing the task edit command to parse annotation
    dates with spaces.
  + Fixed bug #433, making task command output more consistent.

NEWS

@@ -2,7 +2,7 @@
 New Features in task 1.9.3
 
   - Start and stop times for a task can now be recorded as annotations.
-  - Special tags 'nocolor' and 'nonag'.
+  - Special tags 'nocolor', 'nocal' and 'nonag'.
 
   Please refer to the ChangeLog file for full details.  There are too many to
   list here.

doc/man/task.1

@@ -275,8 +275,9 @@ Certain tags (called 'special tags'), can be used to affect the way tasks are
 treated.  For example, is a task has the special tag 'nocolor', then it is
 exempt from all color rules.  The supported special tags are:
 
-    +nocolor     Disable color rules processing for this task.
-    +nonag       Completion of this task suppresses all nag messages.
+    +nocolor     Disable color rules processing for this task
+    +nonag       Completion of this task suppresses all nag messages
+    +nocal       This task will not appear on the calendar
 
 .TP
 .B project:<project-name>

src/report.cpp

@@ -1927,6 +1927,7 @@ std::string renderMonths (
           foreach (task, all)
           {
             if (task->getStatus () == Task::pending &&
+                !task->hasTag ("nocal")             &&
                 task->has ("due"))
             {
               std::string due = task->get ("due");
@@ -2063,7 +2064,8 @@ int handleReportCalendar (std::string &outs)
       {
         if (task->getStatus () == Task::pending)
         {
-          if (task->has ("due"))
+          if (task->has ("due") &&
+              !task->hasTag ("nocal"))
           {
             ++countDueDates;
             Date d (atoi (task->get ("due").c_str ()));