Update the tools used by perl to be defined in the perl script.

The tools were fixed installing specific versions, but that's not a
lot of good if you're trying to allow the environment to be generic.
The code has been pinched from the Python common code, which allows
the configuration to be used to set up the versions of the tools
that are to be used.

common.perl

@@ -5,6 +5,21 @@
 
 set -eo pipefail
 
+# Defaults for the tools we shall use
+perl_tool_coverage='cover'
+perl_tool_lint='perlcritic'
+
+# Default versions of the tools
+perl_toolversion_cover='1.25'
+perl_toolversion_perlcritic='1.126'
+
+# And the definitions of what we need in requirements
+perl_tool_coverage_1_25='Devel::Cover@1.25'
+perl_tool_perlcritic_1_126="
+PPI@1.220
+Perl::Critic@1.126
+Perl::Critic::Pulp@93
+"
 
 ##
 # Is perl active for this action?
@@ -58,6 +73,16 @@ function perl_environment() {
     source "${scripts}/perl-env" -e "${root}/perllib"
 }
 
+function perl_tool_requirements() {
+    local action="$1"
+    local reqs
+    reqs="$(tool_config_expansion perl "$action")"
+    local req
+    for req in $reqs ; do
+        echo -n " +$req"
+    done
+}
+
 function perl_environment_test() {
     perl_environment +PadWalker@2.2 \
                      "${root}/cpan.txt" \
@@ -66,19 +91,23 @@ function perl_environment_test() {
 }
 
 function perl_environment_coverage() {
-    perl_environment +PadWalker@2.2 +Devel::Cover@1.25 \
+    perl_environment +PadWalker@2.2 \
                      "${root}/cpan.txt" \
                      "${root}/cpan-test.txt" \
                      "${root}/cpan-coverage.txt" \
                      "${scripts}/cpan-test.txt" \
-                     "${scripts}/cpan-coverage.txt"
+                     "${scripts}/cpan-coverage.txt" \
+                     $(perl_tool_requirements coverage)
 }
 
 function perl_environment_lint() {
-    perl_environment +PadWalker@2.2 +Perl::Critic@1.126 +PPI@1.220 \
+    perl_environment +PadWalker@2.2 \
                      "${root}/cpan.txt" \
+                     "${root}/cpan-test.txt" \
                      "${root}/cpan-lint.txt" \
-                     "${scripts}/cpan-lint.txt"
+                     "${scripts}/cpan-test.txt" \
+                     "${scripts}/cpan-lint.txt" \
+                     $(perl_tool_requirements lint)
 }