allow concat::fragment target param to be an arbitrary string

Revert validation of the target param as an absolute path and allow it to be an
arbitrary string.  This is so the

    concat { <foo>: path => ...  }
    concat::fragment { ...: target => <foo> }

association may be symbolic as long as concat path param is specified.  This
should resolve the symbolic name regression introduced in:
https://github.com/puppetlabs/puppetlabs-concat/commit/eaf84079

manifests/fragment.pp

@@ -35,7 +35,7 @@ define concat::fragment(
     $group   = undef,
     $backup  = undef
 ) {
-  validate_absolute_path($target)
+  validate_string($target)
   validate_re($ensure, '^$|^present$|^absent$|^file$|^directory$')
   validate_string($content)
   validate_string($source)

spec/system/symbolic_name_spec.rb

@@ -0,0 +1,35 @@
+require 'spec_helper_system'
+
+describe 'symbolic name' do
+  pp="
+    concat { 'not_abs_path':
+      path => '/tmp/file',
+    }
+
+    concat::fragment { '1':
+      target  => 'not_abs_path',
+      content => '1',
+      order   => '01',
+    }
+
+    concat::fragment { '2':
+      target  => 'not_abs_path',
+      content => '2',
+      order   => '02',
+    }
+  "
+
+  context puppet_apply(pp) do
+    its(:stderr) { should be_empty }
+    its(:exit_code) { should_not == 1 }
+    its(:refresh) { should be_nil }
+    its(:stderr) { should be_empty }
+    its(:exit_code) { should be_zero }
+  end
+
+  describe file('/tmp/file') do
+    it { should be_file }
+    it { should contain '1' }
+    it { should contain '2' }
+  end
+end

spec/unit/defines/concat_fragment_spec.rb

@@ -44,22 +44,30 @@ describe 'concat::fragment', :type => :define do
     end
   end
 
-  context 'target =>' do
-    context '/etc/motd' do
-      it_behaves_like 'fragment', 'motd_header', {
+  context 'title' do
+    ['0', '1', 'a', 'z'].each do |title|
+      it_behaves_like 'fragment', title, {
         :target  => '/etc/motd',
       }
     end
+  end # title
 
-    ['./etc/motd', 'etc/motd', false].each do |target|
+  context 'target =>' do
+    ['./etc/motd', 'etc/motd', 'motd_header'].each do |target|
       context target do
-        let(:title) { 'motd_header' }
-        let(:facts) {{ :concat_basedir => '/tmp' }}
-        let(:params) {{ :target => target }}
+        it_behaves_like 'fragment', target, {
+          :target  => '/etc/motd',
+        }
+      end
+    end
 
-        it 'should fail' do
-          expect { should }.to raise_error(Puppet::Error, /is not an absolute path/)
-        end
+    context 'false' do
+      let(:title) { 'motd_header' }
+      let(:facts) {{ :concat_basedir => '/tmp' }}
+      let(:params) {{ :target => false }}
+
+      it 'should fail' do
+        expect { should }.to raise_error(Puppet::Error, /is not a string/)
       end
     end
   end # target =>