Allow pre-release versions on tagged final

If the current version is a final version, we previously did not allow
you to do anything besides rebuild as the current version or increment
to another final version.

While this isn't a recommended option, some people want to be able to
release pre-releases from the same commit that was already released.

There isn't anything critical in reckon depending on preventing this
kind of release, so it seems OK to allow.

reckon-core/src/main/java/org/ajoberstar/reckon/core/Reckoner.java

@@ -71,12 +71,6 @@ public Version reckon() {
       throw new IllegalStateException("Reckoned version " + reckoned + " is (and cannot be) less than base version " + inventory.getBaseVersion());
     }
 
-    inventory.getCurrentVersion().ifPresent(current -> {
-      if (inventory.isClean() && current.isFinal() && !reckoned.isFinal()) {
-        throw new IllegalStateException("Cannot re-release a final version " + current + " as a pre-release: " + reckoned);
-      }
-    });
-
     return reckoned;
   }
 

reckon-core/src/test/groovy/org/ajoberstar/reckon/core/ReckonerTest.groovy

@@ -163,7 +163,7 @@ class ReckonerTest extends Specification {
     reckonSnapshot(inventory, 'major', 'final') == '2.0.0'
   }
 
-  def 'if current version is present and normal, repo is clean, not allowed to release an incremented pre-release stage'() {
+  def 'if current version is present and normal, repo is clean, allowed to release an incremented pre-release stage'() {
     given:
     VcsInventory inventory = new VcsInventory(
       'abcdef',
@@ -175,28 +175,9 @@ class ReckonerTest extends Specification {
       [] as Set,
       [Version.valueOf('1.2.2'), Version.valueOf('1.2.3')] as Set
     )
-    when:
-    reckonStage(inventory, null, 'rc')
-    then:
-    thrown(IllegalStateException)
-  }
-
-  def 'if current version is present and normal, repo is clean, not allowed to release an incremented snapshot'() {
-    given:
-    VcsInventory inventory = new VcsInventory(
-      'abcdef',
-      true,
-      Version.valueOf('1.2.3'),
-      Version.valueOf('1.2.3'),
-      Version.valueOf('1.2.3'),
-      1,
-      [] as Set,
-      [Version.valueOf('1.2.2'), Version.valueOf('1.2.3')] as Set
-    )
-    when:
-    reckonSnapshot(inventory, null, 'snapshot')
-    then:
-    thrown(IllegalStateException)
+    expect:
+    reckonStage(inventory, null, 'rc') == '1.3.0-rc.1'
+    reckonSnapshot(inventory, null, 'snapshot') == '1.3.0-SNAPSHOT'
   }
 
   def 'if current version is present and pre-release, repo is clean, allowed to release a higher normal pre-release'() {