Allow setting custom make error pattern
Allow setting custom make error pattern

The current pattern used by the commands `make-next` and `make-prev`
are not suitable for all usages.

For example the go compiler will not suffix errors with `error: ` and is
not usable with these functions. This change allows the user to define
a custom error pattern, instead of having to work around the error (for
example using sed to insert the `error: ` suffix).

What do you think of this? I have not followed the current convention
of having options without separators (like `makecmd`). Also this does
not feel to be the right solution because the pattern has to be set at
global level.

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