make docs doesn't regenerate docs correctly after changing API doc comments in jaxp sources

build the jdk; call make docs; change some API comments in jaxp; call make docs => the docs are not updated.

If you change some API comments in jaxp source and call 'make docs' at root level, the previously generated docs are not correctly updated. I suspect this because only jaxp classes are reimported when building the jdk tree. I see these traces:

$ make docs
Building Java(TM) for target 'docs' in configuration 'macosx-x86_64-normal-server-release'

## Starting langtools
## Finished langtools (build time 00:00:01)

## Starting hotspot
## Finished hotspot (build time 00:00:01)

## Starting corba
## Finished corba (build time 00:00:01)

## Starting jaxp
Compiling 1881 files for BUILD_JAXP
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
Modifying jaxp/dist/lib/classes.jar
  updating 2356 files
## Finished jaxp (build time 00:00:46)

## Starting jaxws
## Finished jaxws (build time 00:00:01)

## Starting jdk
Importing JAXP classes.jar
Importing JAXWS classes.jar
Importing LANGTOOLS classes.jar
## Finished jdk (build time 00:00:13)

There's no mention of 'Importing JAXP src.zip' - I suspect it's what is causing the issue.

The workaround is to remove build/<os-platform>/jaxp before calling make docs.