libdatrwxx [TASK]: add mseed usage information

add text regarding "usec" consitency check

src/libs/libdatrwxx/mseed/imseedstream_help.cc

@@ -28,11 +28,12 @@
  *
  * REVISIONS and CHANGES 
  *  - 05/07/2016   V1.0   Thomas Forbriger
+ *  - 12/07/2016   V1.1   thof: new consistency check ID "usec"
  * 
  * ============================================================================
  */
 #define DATRW_IMSEEDSTREAM_HELP_CC_VERSION \
-  "DATRW_IMSEEDSTREAM_HELP_CC   V1.0"
+  "DATRW_IMSEEDSTREAM_HELP_CC   V1.1"
 
 #include <datrwxx/mseed.h>
 #include <datrwxx/formatmodifier.h>
@@ -154,6 +155,11 @@ namespace datrw {
       mh << "is compared against the value of the reverse\n";
       mh << "integration constant as provided in the first data\n";
       mh << "frame of the record. Both must be identical.\n";
+      mh(key::usec)
+        << "The SEED Reference Manual (Version 2.4, August, 2012, page 124)\n";
+      mh << "specifies the usec field in [1001] Data Extension Blockette:\n";
+      mh << "The recommended value is from -50 to +49 usecs. At the users\n";
+      mh << "option, this value may be from 0 to +99 usecs.\n";
       mh(key::all)
         << "Select all consistency checks\n";
       os << "Consistency checks will be selected upon a substring match\n"