src/channel-type.c (guile_ssh_make_channel): Cleanup the code.
src/threads.{c,h}, src/Makefile.am: Fix several bugs.

* src/threads.c, src/threads.h: Fix a bug with variable
  initialization: use constant value to initialize SSH threads
  state.
* src/Makefile.am (libguile_ssh_la_SOURCES): Add missed files.
  (libguile_ssh_la_LDFLAGS): Add missed flags.