In prepend_path, append_path: never include current working directory.

Some Linux distributions have a dynamic loader that treats empty components of
$LD_LIBRARY_PATH (e.g. the second path component in an LD_LIBRARY_PATH of
"/usr/local/lib:") as if they contained a single dot. This leads to serious
crashing if the current working directory happens to be one of the initrd `lib`
directories. Oddly enough, it appears Slackware's glibc/ld.so is patched to
ignore empty path components and actually *requires* a literal dot in order to
load libraries from the current working directory.

Interpreting "" as "." is fucking brain damaged. I can't imagine why ignoring
empty path components isn't the default. Scripts everywhere do things like
`export PATH="/foo:$PATH"` on the assumption that empty components will be
ignored, only to break catastrophically when a directory they `cd` in to happens
to contain the wrong shared library.