Update README and messages

Author: Matthias Koeppe

pkgs/sage-conf/README.rst

@@ -78,10 +78,20 @@ sage_conf in the SageMath distribution
 The original version of the distribution package ``sage_conf`` is used
 internally in the SageMath distribution.  It is provided in the directory
 `pkgs/sage-conf <https://github.com/sagemath/sage/tree/develop/pkgs/sage-conf/>`_.
-This version of the package is generated by the Sage distribution's ``configure``
+This version of the package is generated by the Sage distribution's ``./configure``
 script.
 
 
+sage_conf for conda
+-------------------
+
+The version of the distribution package in the directory
+`pkgs/sage-conf_conda <https://github.com/sagemath/sage/tree/develop/pkgs/sage-conf_conda/>`_
+is used in an experimental installation method of SageMath, where all packages
+are provided by conda.  This method is described in
+https://doc.sagemath.org/html/en/installation/conda.html#using-conda-to-provide-all-dependencies-for-the-sage-library-experimental
+
+
 sage_conf in downstream distributions
 -------------------------------------
 

pkgs/sage-conf_conda/setup.py

@@ -34,12 +34,12 @@ def run(self):
             if os.system(cmd) != 0:
                 if os.path.exists(os.path.join(SAGE_ROOT, 'config.status')):
                     print("Warning: A configuration has been written, but the configure script has exited with an error. "
-                          "Carefully check any error messages before continuing.")
+                          "Carefully check any messages above before continuing.")
                 else:
                     print(f"Error: The configure script has failed; this may be caused by missing build prerequisites.")
                     sys.stdout.flush()
                     PREREQ_SPKG = "_prereq bzip2 xz libffi"  # includes python3 SPKG_DEPCHECK packages
-                    os.system(f'cd {SAGE_ROOT} && export SYSTEM=$(build/bin/sage-guess-package-system 2>/dev/null) && export PACKAGES="$(build/bin/sage-get-system-packages $SYSTEM {PREREQ_SPKG})" && [ -n "$PACKAGES" ] && echo "You can install the required build prerequisites using the following shell command" && echo "" && build/bin/sage-print-system-package-command $SYSTEM --verbose --sudo install $PACKAGES && echo ""')
+                    os.system(f'cd {SAGE_ROOT} && export PACKAGES="$(build/bin/sage-get-system-packages conda {PREREQ_SPKG})" && [ -n "$PACKAGES" ] && echo "You can install the required build prerequisites using the following shell command" && echo "" && build/bin/sage-print-system-package-command conda --verbose --sudo install $PACKAGES && echo ""')
                     raise SetupError("configure failed")
 
         # In this mode, we never run "make".