covr ignores .covrignore file

[mpadge]

In almost any environment (e.g. rocker/tidyverse container), direct call of package_coverage ignores .covignore, while calling via withr does not:

cd /home/
git clone https://github.com/HaoZeke/fastMatMR # A repo with a `.covrignore` file
R
> path <- "/home/fastMatMR"
> c1 <- covr::package_coverage()
> c2 <- withr::with_dir(path, covr::package_coverage())

Result: c1 ignores .covrignore, and gives low coverage, while c2 respects it and gives much higher.

[mpadge]

This happens because these lines presume call is made in root directory:

covr/R/exclusions.R

Lines 210 to 213 in caed186

	if (!file.exists(file)) {
	return(NULL)
	}
	lines <- readLines(file)

but that of course need not necessarily be so. Need to fix that function so that file is a full path.