Part of a wider change.

Remove some system headers which are needed to be found portably.

On i386 view_split_begin_y() computed a value slightly different than on other arches, breaking the regress. Casting HSPLIT_SCALE as float unbreaks it. Diff from jamsek, committing on his behalf. Thanks!

we can't open arbitrary files after unveil(), and that's a feature! So, open it early and truncate it before use just in case screendump() ends up being called more than once. ok/tweak stsp, ok jamsek

ok stsp, jamsek

as it might not be there (for e.g. if ran under cron). Reuse instead /dev/null since it's not expected to get input from stdin. ok jamsek

ok and README update by jamsek

ncurses(3) will use the line drawing characters from the VT100 alternate graphics character set if the terminal supports this as indicated by termcap/terminfo, otherwise it will fall back to ASCII replacement characters. ok jamsek stsp

Add count instruction to the test harness to simulate count modifier compound keys (e.g., 11j), and add basic tests for the tree view. ok stsp@

Also, overwrite - and | unconditionally when capturing screen dumps, and unset TOG_COLORS and TOG_DIFF_ALGORITHM in regress setup. All tweaks suggested by naddy@ ok stsp@

As suggested by stsp, rather than busy wait in the view loop, use pthread conditions to wait for the blame thread to signal completion before drawing the screen. We can add more conditions for other views when needed, but by keeping the general WAIT_FOR_UI instruction and flag, this should make their use context-dependent so we won't need more test harness WAIT_* instructions. ok stsp@

Requested by James Cook

Problem reported by James Cook with reproduction scripts Regression test case by jamsek, as a simplified version of James' scripts fix tested + ok jamsek