Keep Curl Bootstrap Working With http:// (#3113)

* Add comments documenting problems in recent versions of NetCDF.
* Add comments to packages required to install curl.

var/spack/repos/builtin/packages/curl/package.py

@@ -30,6 +30,7 @@ class Curl(Package):
     transferring data with URL syntax"""
 
     homepage = "http://curl.haxx.se"
+    # URL must remain http:// so Spack can bootstrap curl
     url      = "http://curl.haxx.se/download/curl-7.46.0.tar.bz2"
 
     version('7.52.1', 'dd014df06ff1d12e173de86873f9f77a')

var/spack/repos/builtin/packages/openssl/package.py

@@ -33,6 +33,7 @@ class Openssl(Package):
        Layer Security (TLS) and Secure Sockets Layer (SSL) protocols.
        It is also a general-purpose cryptography library."""
     homepage = "http://www.openssl.org"
+    # URL must remain http:// so Spack can bootstrap curl
     url      = "http://www.openssl.org/source/openssl-1.0.1h.tar.gz"
     list_url = "https://www.openssl.org/source/old/"
     list_depth = 2

var/spack/repos/builtin/packages/perl/package.py

@@ -35,6 +35,7 @@ class Perl(Package):
     """Perl 5 is a highly capable, feature-rich programming language with over
        27 years of development."""
     homepage = "http://www.perl.org"
+    # URL must remain http:// so Spack can bootstrap curl
     url      = "http://www.cpan.org/src/5.0/perl-5.24.1.tar.gz"
 
     version('5.24.1', '765ef511b5b87a164e2531403ee16b3c')

var/spack/repos/builtin/packages/zlib/package.py

@@ -30,6 +30,7 @@ class Zlib(AutotoolsPackage):
        data-compression library."""
 
     homepage = "http://zlib.net"
+    # URL must remain http:// so Spack can bootstrap curl
     url = "http://zlib.net/fossils/zlib-1.2.10.tar.gz"
 
     version('1.2.11', '1c9f62f0778697a09d36121ead88e08e')