Absolute path in .gitignore are interpreted from the current directory instead of the .gitignore file path

[Congelli501]

Lines starting with a "/" in .gitignore files should be interpreted as being relative the the .gitignore file path, but they are interpreted as beeing relative to cwd for ag.

How to reproduce:

cd /tmp
rm -fr test
mkdir test
cd test
mkdir -p subdir/dir1
echo 'aaa' > subdir/dir1/f

cat > .gitignore << 'EOF'
/dir1
EOF

# Not working -> dir1 should be ignored
ag aaa .
cd subdir

# Working as cwd is the location of the .gitignore file -> dir1 is ignored
ag aaa .