Edit longnum_multinum_sum to use plain array instead of C++'s queue.
Edit longnum_multiply to use new interface of longnum_multinum_sum.
Edit longnum_engine-multinum-sum demo program to use new interface of longnum_multinum_sum.
Opps, I forget to move the num_curr[i] (in longnum_multinum_sum).
Eliminate C++'s #include.
Rename longnum_engine.cpp to longnum_engine.c.

This is to use C compiler. Also, change the final .so compiler to $(CC).
Rename longnum_engine-multinum-sum.cpp to longnum_engine-multinum-sum.c.

Also, change demo-program/Makefile to reflect this.
Make longnum_engine-multinum-sum demo program to support longnum (pun intended).

Old version isn't support number that is bigger than "unsigned int". This change is introduced to fix this.
Merge branch 'master' into autotools
Edit Makefile.am to reflect file name change.
Edit remove-autogen.sh to also delete "compile".