install fails if aria2c has dir configured

[brbsix]

When running pyenv install, I encountered the following error:

Downloading pypy3-2.4-linux_x86_64-portable.tar.bz2...
-> https://bitbucket.org/squeaky/portable-pypy/downloads/pypy3-2.4-linux_x86_64-portable.tar.bz2
/home/user/.pyenv/plugins/python-build/bin/python-build: line 230: pushd: pypy3-2.4-linux_x86_64-portable: No such file or directory

BUILD FAILED (Ubuntu 15.04 using python-build 20160509-26-g216244f)

Inspect or clean up the working tree at /tmp/python-build.20160608033247.24622
Results logged to /tmp/python-build.20160608033247.24622.log

Last 10 log lines:
======+====+===========+=======================================================
486ae0|OK  |   589KiB/s|/home/user/Downloads/aria2/pypy3-2.4-linux_x86_64-portable.tar.bz2

Status Legend:
(OK):download completed.
mv: cannot stat ‘pypy3-2.4-linux_x86_64-portable.tar.bz2’: No such file or directory
tar (child): pypy3-2.4-linux_x86_64-portable.tar.bz2: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now

I don't have the logs or set -x output handy, but I believe this is due aria2c's configuration file $HOME/.aria2/aria2.conf with the following entry:

dir=/home/user/Downloads/aria2

I can imagine this will cause issues for people in the future...