Fix errors in gmtspatial related to -N

[PaulWessel]

See #7745 for background. There were three problems in gmt spatial -N that have been addressed:

1. Failed to exclude features completely outside the polygon
2. Flawed implementation of +a could easily failed if the middle point was outside
3. Failed to turn off output from segments that failed the test

I also added a simple text test called test/gmtspatial/inout_features.sh

Closes #7745.

[macpurity]

I appreciate that this issue has been closed, but I now see error messages with -N when specifying +p, without setting a "start" value.

The on-line documentation indicates the +p will default to zero, but this command (part of a much larger piece of code) causes an error message:

echo ${flonlat[@]} | gmt gmtspatial -N${usbdy80k}+p+r

What this line does is determine whether a lon,lat point falls inside a simple conterminous boundary of the USA. This command used to work, but now it issues the following:

gmtspatial [ERROR]: Option -N: Modifier +p given no value

The easy work-around is to specify +p0. Which is what I did to get the script to work properly. If there no longer a default value, then the on-line documentation should be changed.

The on-line documentation currently reads: "or it is assigned the running number that is initialized to start [0]." This suggests that zero is the default value if none is provided.

[PaulWessel]

Fixed in #8039.

[macpurity]

Thanks, Paul. That did the trick!