SI-6424 Scaladoc: Use mapNodes.get(_) to avoid NoSuchElementException

Use mapNodes.get(_) instead of mapNodes(_) to avoid NoSuchElementException.
[backport #1727] SI-7359 cyclic nested java class

The original commit message (from 54a84a36d5):

SI-6548 reflection correctly enters jinners

When completing Java classes, runtime reflection enumerates their
fields, methods, constructors and inner classes, loads them and
enters them into either the instance part (ClassSymbol) or the
static part (ModuleSymbol).

However unlike fields, methods and constructors, inner classes don't
need to be entered explicitly - they are entered implicitly when
being loaded.

This patch fixes the double-enter problem, make sure that enter-on-load
uses the correct owner, and also hardens jclassAsScala against double
enters that can occur in a different scenario.
Prevent slash duplication.

Don't add trailing slash to external doc URL if it already ends with
one.
SI-7486 regression in implicit resolution.

What a touchy beast the compiler is.
Merge pull request #2553 from paulp/issue/7486

SI-7486 regression in implicit resolution.
SI-7201 scaladoc url in scala-(library,actors,swing,reflect) pom

The project/properties/info.apiURL pom property is used by SBT
to link to an artifact's scaladoc.

For scala library version $v, the url is http://www.scala-lang.org/api/$v/
Note that actors, reflect and swing are included in the library docs in 2.10.x.
Merge pull request #2536 from adriaanm/ticket-7359

[backport #1727] SI-7359 cyclic nested java class
Merge pull request #2549 from vigdorchik/slash_slash

Prevent slash duplication.
Merge pull request #2530 from kzys/jira-6424

SI-6424 Scaladoc: Use mapNodes.get(_) to avoid NoSuchElementException
Merge pull request #2540 from adriaanm/ticket-7201

SI-7201 scala-library's pom points to scaladoc url