Bug 39720 Adding external jar to the Build Path of an existing Java project [build path]
When adding an external jar file to an existing Java project, the "Setting Build Path" error dialog is displayed. The dialog displays the text "An error occured while setting the build path. Reason: /usr does not exist". The jar to be added in this case is located in the /usr/local/bin/ directory. I am working with the release 2.1 build for linux.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/CPListElement.java
return JavaCore.newSourceEntry(fPath, exclusionPattern, outputLocation);
			case IClasspathEntry.CPE_LIBRARY:
				IPath attach= (IPath) getAttribute(SOURCEATTACHMENT);
				return JavaCore.newLibraryEntry(fPath, attach, null, isExported());
			case IClasspathEntry.CPE_PROJECT:
				return JavaCore.newProjectEntry(fPath, isExported());
			case IClasspathEntry.CPE_CONTAINER:
				return JavaCore.newContainerEntry(fPath, isExported());
			case IClasspathEntry.CPE_VARIABLE:
				IPath varAttach= (IPath) getAttribute(SOURCEATTACHMENT);
				return JavaCore.newVariableEntry(fPath, varAttach, null, isExported());
			default:
				return null;
		}
	}
	
	/**
	 * Gets the classpath entry path.
	 * @see IClasspathEntry#getPath()
	 */
	public IPath getPath() {
		return fPath;
	}
	/**
	 * Gets the classpath entry kind.
	 * @see IClasspathEntry#getEntryKind()
	 */	
	public int getEntryKind() {
		return fEntryKind;
	}