curl-devel renamed to libcurl-devel

The package curl-devel has been renamed to libcurl-devel in Red Hat
relase 6
Merge pull request #1280 from alenzen/master

curl-devel has been renamed to libcurl-devel since RHEL 6
Credit Alessandro Lenzen

[ci:skip]
Bump version to 4.0.51
chdir() after chroot()ing.

We currently do not support chrooting so the code is never invoked,
but not chdir()'ing after chroot() can result in a security vulnerability,
so I'll add the chdir() code anyway to prevent future mistakes. Thanks
to darix for reporting this.
Bump version to 4.0.52

[ci:skip]
Merge branch 'master' into eternal_sunset

Conflicts:
	CHANGELOG