setting from --enable-debug, allowing again to build c-ares independently

  out of the CVS tree.

  For the c-ares library option --enable-debug enables debug build features

  which are _not_ related with memory tracking. For the c-ares library when

  --enable-debug is given it does not enable the memory tracking feature. If

  you wish to enable the curl debug memory tracking you must use configure

  option --enable-curldebug explicitily to do so.

  Internally, definition of preprocessor symbol DEBUGBUILD restricts code

  which is only compiled for debug enabled builds. And symbol CURLDEBUG is

  used to differentiate code which is _only_ used for memory tracking.

* May 19 2009 (Yang Tse)

- Introduced ares_library_init() and ares_library_cleanup() functions.