* heap.cc (heap_init): Be slightly more aggressive when trying to allocate

* heap.cc (heap_init): Be slightly more aggressive when trying to allocate
heap.  Change fatal error to avoid confusion with cygheap.
* spawn.cc (linebuf::finish): New function.
(linebuf::add): Cosmetic change.
(spawn_guts): Only avoid building windows command line if the program being
executed was actually mounted with -X.  Don't return E2BIG if we hit the 32K
size and we're executing a detected cygwin program.  Just silently truncate the
windows command line, instead.