Add an install target to all makefiles.  For the import build, the top-level Makefile now does two passes: (1) builds libapp.a, then (2) installs the programs (not yet finished)

Beginning of logic that will, hopefully, all me to build applications against a NuttX export package (vs. the nuttx/ source tree).

The ELF test/example has been extended so the individual ELF test programs can link against the SYSCALL library (if it is available) or against the C library to eliminate or minimize the need for symbol tables (2014-8-29).