fix situation where AUR package cannot build as is from AUR, but user has the package installed

[sigboe]

Note this also cleans up how errors are handled and presented. For the purpouse of having a warning that just continues as well as an error that exits the script.

[sigboe]

This PR along with #19 will allow users who already have icamerasrc-git installed to install or update the driver.

@stefanpartheym I am open to discussion how we proceed with icamerasrc-git intel has introduced a bug at this line in this file that breaks compiling. The compiler says the function is passing too many arguments, removing the second (newly added argument) fixes compiling. I have not tested if any functionality is lost by doing this. This bug was introduced in commit fe733e7 at April 3. And has issue intel/icamerasrc#32 opened at April 6. Our issue #18 was opened at April 18. Do you want us to roll our own PKGBUILD file or something? 17841ab compiles successfully and can be compiled by replacing the source array in the PKGBUILD to fetch "git+${url}.git#commit=17841ab6249aaa69bd9b3959262bf182dee74111" instead.