Define R_NO_REMAP in all the source files under src/main/jit, to decrease the
number of macros polluting the namespace in the JIT code.
Change the order of #include statements to include system and llvm headers
before any R headers.  This helps limit the damage done by the remaining macros
in the R headers.
Add a memory manager to the JIT code.

The memory manager adds support at JIT link time for lookups of R Symbols,
BuiltInFunctions, and any other global objects that the compiler registers.
Fixed gross errors in the JIT exception handling code that caused it to fail
in even the simplest of cases.
Set LD_LIBRARY_PATH for the unit tests, so that the dynamic linker can find
libRblas.so.