Detect double declarations

The compiler passes would ignore multiple declarations of a references within the same block:

    var foo = 1
    var foo = 2

The problem would only be detected at bytecode-generation time with ASM throwing out-of-bounds
exceptions.

This commit provides a fix for that. It also introduces the marking of local references as
synthetic, like those generated for loop iterators. This is used in the problem detection since
these variables behave marginally differently from those defined by programmers.
Allow lax imports

Lax imports widen the range of valid imports in Golo, as in:

    import java.util
    function foo = -> Arrays.asList(1, 2, 3)

or,

    import java
    function foo = -> util.Arrays.asList(1, 2, 3)

Previously, one would have had to use either of the following constructs:

    import java.util.Arrays
    function foo = -> Arrays.asList(1, 2, 3)

or,

    import java.util.Arrays
    function foo = -> asList(1, 2, 3)
Include java.lang in the default imports
Merge pull request #122 from jponge/wip/lax-imports

Allow lax imports
OS-dependent newline caused test to fail on Windows

Fixes #123.
NPE on duplicate synthetic references
Allow JDK 7 to fail in build matrix

Some OpenJDK 7 and Oracle JDK 7 releases in the wild are broken with
respect to invokedynamic. This is affecting other projects like Groovy.

This introduces a Travis-CI build matrix where Oracle JDK 8 is the sole
reference. This will also let us know if JDK 7 releases get eventually
fixed at some hypothetical point in the future. Who knows?
Filtering out 'private' struct members
Allow same-module code to call struct private elements
Allow same-module augmentations to access struct private elements
Tests within module
Tests outside the defining module
Documentation for private struct members
Merge pull request #126 from jponge/wip/structs-encapsulation

Structs encapsulation
Promise early sketch
Blocking get
Blocking get simplifications
Future early sketch
More Promise / Future test coverage
Refactoring