make curl-minimal require a new enough version of libcurl

At the same time relax the dependency of curl on libcurl to support
running old curl on top of new libcurl but not vice versa.

curl.spec

@@ -1,7 +1,7 @@
 Summary: A utility for getting files from remote servers (FTP, HTTP, and others)
 Name: curl
 Version: 7.54.0
-Release: 3%{?dist}
+Release: 4%{?dist}
 License: MIT
 Group: Applications/Internet
 Source: https://curl.haxx.se/download/%{name}-%{version}.tar.lzma
@@ -64,7 +64,8 @@ BuildRequires: perl(vars)
 BuildRequires: valgrind
 %endif
 
-Requires: libcurl%{?_isa} = %{version}-%{release}
+# using an older version of libcurl could result in CURLE_UNKNOWN_OPTION
+Requires: libcurl%{?_isa} >= %{version}-%{release}
 
 # require at least the version of libssh2 that we were built against,
 # to ensure that we have the necessary symbols available (#525002, #642796)
@@ -111,6 +112,9 @@ Provides: curl = %{version}-%{release}
 Conflicts: curl
 RemovePathPostfixes: .minimal
 
+# using an older version of libcurl could result in CURLE_UNKNOWN_OPTION
+Requires: libcurl%{?_isa} >= %{version}-%{release}
+
 %description -n curl-minimal
 This is a replacement of the 'curl' package for minimal installations.  It
 comes with a limited set of features compared to the 'curl' package.  On the
@@ -292,6 +296,9 @@ install -m 644 docs/libcurl/libcurl.m4 $RPM_BUILD_ROOT%{_datadir}/aclocal
 %{_libdir}/libcurl.so.[0-9].[0-9].[0-9].minimal
 
 %changelog
+* Thu May 04 2017 Kamil Dudka <kdudka@redhat.com> 7.54.0-4
+- make curl-minimal require a new enough version of libcurl
+
 * Thu Apr 27 2017 Kamil Dudka <kdudka@redhat.com> 7.54.0-3
 - switch the TLS backend back to OpenSSL (#1445153)