Skip creating shims for system executables bundled with Anaconda (fixes #594, #599)

With this, we'd be able to remove a hook script for `pyenv which`
eventually.

pyenv.d/rehash/anaconda.bash

@@ -0,0 +1,123 @@
+# Anaconda comes with binaries of system packages (e.g. `openssl`, `curl`).
+# Creating shims for those binaries will prevent pyenv users to run those
+# commands normally when not using Anaconda.
+#
+# This hooks is intended to skip creating shims for those executables.
+
+conda_exists() {
+  shopt -s nullglob
+  local condas=($(echo "${PYENV_ROOT}/versions/"*"/bin/conda" "${PYENV_ROOT}/versions/"*"/envs/"*"/bin/conda"))
+  shopt -u nullglob
+  [ -n "${condas}" ]
+}
+
+conda_shims() {
+  ## curl
+  cat <<EOS
+curl
+curl-config
+EOS
+
+  ## fontconfig
+  cat <<EOS
+fc-cache
+fc-cat
+fc-list
+fc-match
+fc-pattern
+fc-query
+fc-scan
+fc-validate
+EOS
+
+  ## freetype
+  cat <<EOS
+freetype-config
+EOS
+
+  ## libpng
+  cat <<EOS
+libpng-config
+EOS
+
+  ## openssl
+  cat <<EOS
+openssl
+EOS
+
+  ## qtchooser
+  cat <<EOS
+assistant
+designer
+lconvert
+linguist
+lrelease
+lupdate
+moc
+pixeltool
+qcollectiongenerator
+qdbus
+qdbuscpp2xml
+qdbusviewer
+qdbusxml2cpp
+qhelpconverter
+qhelpgenerator
+qmake
+qmlplugindump
+qmlviewer
+qtconfig
+rcc
+uic
+xmlpatterns
+xmlpatternsvalidator
+EOS
+
+  ## redis
+  cat <<EOS
+redis-benchmark
+redis-check-aof
+redis-check-dump
+redis-cli
+redis-server
+EOS
+
+  ## sqlite3
+  cat <<EOS
+sqlite3
+EOS
+
+  ## libxml2
+  cat <<EOS
+xml2-config
+EOS
+
+  ## libxslt
+  cat <<EOS
+xslt-config
+EOS
+
+  ## xsltproc
+  cat <<EOS
+xsltproc
+EOS
+
+  # xz-utils
+  cat <<EOS
+xz
+EOS
+}
+
+# Remove conda shims
+filter_conda_shims() {
+  { cat
+    conda_shims
+  } | sort | uniq -c | awk '$1=="1"{print $2}' | tr '\n' ' '
+}
+
+deregister_conda_shims() {
+  registered_shims="$(for shim in $registered_shims; do echo "${shim}"; done | filter_conda_shims)"
+}
+
+if conda_exists; then
+  deregister_conda_shims
+fi