Add M_CANAL flag to indicate which ships can navigate a canal
in a big city. Remove the hard code values for canal from
shp_nav_one_sector() for which ships can navigate a canal.
Set M_CANAL flag in ship_chr_flags[] to match the hard
coding in shp_nav_one_sector().
Update Ship-types.t with new canal flag.
Update Sector-types.t to indicate that cities have canals.
machine-dependencies:
(lwpNewContext): New, factored out of lwpCreate().
(lwpSwitchContext): New, factored out of lwpReschedule().
(LWP_EXTRASTACK, STKALIGN, lwpInitContext, lwpSave, lwpRestore): Move
to arch.c. Remove for UCONTEXT, else static linkage unless macro or
AIX32.
(lwpReschedule): Skip lwpStatus() when not actually switching.
(LwpStackGrowsDown): New.
(lwpInitSystem): Initialize it.
(lwpStackCheck, lwpStackCheckUsed): Use it.
ustack, usize.
(lwpCreate): Initialize them.
(lwpStackCheckInit, lwpStackCheck, lwpStackCheckUsed): Rewrite using
them. lwpStackCheckUsed() was off by LWP_REDZONE when stack grows
down.
(lwpDestroy): Don't bother to clear memory to be freed.
(lwpCreate): Used to allocate one byte more than necessary. The fix
won't save memory (malloc() will add the byte back), it's just clearer
this way.
(lwpCreate): Clean up computation of sp. Rename parameter size to
stacksz.
(lwpCreate): Always compute newp->lowmark and newp->highmark from sp,
not from s. Old code misaligned newp->himark for stacks growing
upward when stack size argument wasn't aligned.
complete declaration to src/lib/lwp/lwpint.h.
(lwpQueue): Move to src/lib/lwp/lwpint.h.
(empth_main, empth_flags): New.
(empth_init): Initialize them.
(empth_create, empth_exit): Use them instead of lwpProc members.
(skipfs): New.
(xuflds, xundump): Use it. Update field scanf stop-sets accordingly.
(xuflds): Update test for good field separator.
(xundump): Fail silently if nothing can be read and no specific table
is expected.
(xundump): Set empfile member cids in addition to fids.
(xundump): Clarify shortcomings: requires EFF_MEM, appends sentinel
always, can't grow dynamic cache.
(xundump): Return table type on success.
