allow whitebox executable to be symlinked

[mholling]

This minor patch causes a fully-resolved path for the whitebox executable to be used when locating the plugins folder. This allows the executable to be symlinked from another location.

I maintain the Whitebox Tools package for MacPorts (a macOS packaging system). As is usual for unix-style packaging systems, MacPorts installs all binaries in a standard location, /opt/local/bin. This causes a problem for the whitebox plugins, whose paths are hard-coded to be in a plugins subdirectory co-located with the main executable. It's not feasible to have such a folder located in a shared directory. Instead I symlink the whitebox_tools binary from another location where it and the plugins subdirectory reside. The submitted patch resolves such a symlink and allows the plugins directory to be successfully located.

[mholling]

OK. I don't understand why you invite contributions if you're not interested in them. I think an open-source/closed-development model would be a better fit for Whitebox Tools. It'd prevent people wasting their time on contributions which are ignored.

[jblindsay]

Hello @mholling, thank you for this PR. I understand your frustration, but I'd ask that you maintain a respectful tone. Please understand that I am doing the best that I can with extremely limited resources and that Whitebox is an enormous project. You are absolutely correct that Whitebox is not like some other OS projects where there are a large number of contributors. Basically, it is a project that is driven by one person, me, and as it grows more complex, it becomes increasingly difficult for me reconcile PRs. For example, for this PR, it may be a small change, but I know from experience that anything involving how file paths are treated in Wb can cause subtle errors on other platforms. Has this change been tested on Linux and Windows? If I accept this PR and it gets released, will I get hundreds of Windows/Linux users complaining that things are now broken? I need to find the time to evaluate it, and frankly time is the one thing that I have the least of. I welcome you PR, but it may not get my attention in the time frame that you would hope for.