MFC r341657 (by imp): Dynamically load .so modules to expand functionality

o Dynamically load all the .so files found in /libexec/nvmecontrol and

/usr/local/libexec/nvmecontrol.

o Link nvmecontrol -rdynamic so that its symbols are visible to the

libraries we load.

o Create concatinated linker sets that we dynamically expand.
o Add the linked-in top and logpage linker sets to the mirrors for them

and add those sets to the mirrors when we load a new .so.

o Add some macros to help hide the names of the linker sets.
o Update the man page.