Fix SemVer version comparison and improve warning

The != operator returns false for strings here; we need x.equals(y).

Author: ctrueden

src/it/delete-other-versions-policy/verify.bsh

@@ -47,4 +47,4 @@ assertTrue("Should not exist: " + newer, !toInstall.exists());
 
 buildLog = readFile(new File(basedir, "build.log"));
 assertTrue("Found other version that is incompatible':\n" + buildLog,
-	buildLog.contains("Found other version that is incompatible"));
+	buildLog.contains("is incompatible according to SemVer"));

src/main/java/org/scijava/maven/plugin/install/AbstractInstallMojo.java

@@ -239,10 +239,12 @@ else if (isBioFormatsArtifact(artifact)) {
 						else {
 							final String otherVersion = group.substring(1);
 							newerVersion = VersionUtils.compare(toInstall, otherVersion) < 0;
-							if (majorVersion(toInstall) != majorVersion(otherVersion)) {
-								getLog().warn(
-									"Found other version that is incompatible according to SemVer: " +
-										otherVersion);
+							final String majorVersionToInstall = majorVersion(toInstall);
+							final String majorVersionOther = majorVersion(otherVersion);
+							if (!majorVersionToInstall.equals(majorVersionOther)) {
+								getLog().warn("Version " + otherVersion + " of " + artifact +
+									" is incompatible according to SemVer: " +
+									majorVersionToInstall + " != " + majorVersionOther);
 							}
 						}
 						if (newerVersion) break;