watch: --enable-watch8bit may be needed, else it may mangle UTF-8 output by commands

[TurtleWilly (Wilhelm Loves Their Turtles)]

By default the watch command seems to mangle UTF8 output:

$ watch echo "MacPortsさん、こんにちは！"

results in:

Every 2.0s: echo MacPortsさん、こんにちは！                                                                                                                                                                     

MacPorts      M-M-M-M

Note that the banner looks OK, but the actual output of the command gets mangled into those "M-M-" stuff.

The configure script has an option to fix that: --enable-watch8bit, I also needed to apply an additional fix in watch.c itself and remove the "ncursesw/" prefix from the ncurses include. Afterwards the output looks as we would expect:

Every 2.0s: echo MacPortsさん、こんにちは！                                                                                                                                                                     

MacPortsさん、こんにちは！