WL#5016: Fix header file include guards

This worklog is an implementation worklog to implement the following:

   - Add header file include guards to all header files that require it.

   - Change any header file include guards that start with _, since that either
     violates the C/C++ standard or is dangerously close to that.

   - Introduce any other changes that are necessary for the system to build
     properly.

   - Other include file guards will be left alone.

No architecture review is needed since this is part of WL#4877.

The patch for this worklog is a re-committed version of a patch already
committed and reviewed for WL#4877.

The format of the include header guards are of the form:

   __INCLUDED

Where  is the name of the package in uppercase letters, and 
is the name of the header file (in uppercase letters) with the extension
removed. However, since the files in the sql/ directory are not yet in a package
and will eventually be moved to a package, we will not use a package name at
this time and just use the form:

    _INCLUDED