Remove leftovers of IRIX port

This removes the remaining pieces of the IRIX port that was removed by
ea91a6be89575095f61ebf36d67c2df98be093db.
Fix doc links in README file to work with new website layout

Per report from Colin 't Hart
doc: Fix typo.

Reported by Thom Brown.
Try again to make pg_isolation_regress work its build directory.

We can't search for the isolationtester binary until after we've set
up the environment, because otherwise when find_other_exec() tries
to invoke it with the -V option, it might fail for inability to
locate a working libpq.  So postpone that step.

Andres Freund
gitattributes: Make syntax compatible with older Git versions

Avoid the use of **, which was only introduced in Git version 1.8.2.
Move variable closer to where it is used

This avoids an unused variable warning on Windows when building without
asserts

From: David Rowley <dgrowleyml@gmail.com>
Fix bug in GIN posting tree root creation.

The root page is filled with as many items as fit, and the rest are inserted
using normal insertions. However, I fumbled the variable names, and the code
actually memcpy'd all the items on the page, overflowing the buffer. While
at it, rename the variable to make the distinction more clear.

Reported by Teodor Sigaev. This bug was introduced by my recent
refactorings, so no backpatching required.
Free ignorelist after each regression test schedule.

It's a trivial amount of RAM held until the end of the regression
test run; but it's probably worth fixing to silence future warnings
from code analyzers.

This was the only memory leak pointed out by clang's static code
analysis tool.
docs:  clarify MVCC introduction to allow for per-statement snapshots
Fix relfilenodemap.c's handling of cache invalidations.

The old code entered a new hash table entry first, then scanned
pg_class to determine what value to fill in, and then populated the
entry.  This fails to work properly if a cache invalidation happens
as a result of opening pg_class.  Repair.

Along the way, get rid of the idea of blowing away the entire hash
table as a method of processing invalidations.  Instead, just delete
all the entries one by one.  This is probably not quite as cheap but
it's simpler, and shouldn't happen often.

Andres Freund
Fix isolation check for MSVC to handle recent changes.
Clarify CREATE FUNCTION documentation about handling of typmods.

The previous text was a bit misleading, as well as unnecessarily vague
about what information would be discarded.  Per gripe from Craig Skinner.
Fix whitespace
Fix incorrect column name in psql \d code.

pg_index.indisreplident had at one time in its development been called
indisidentity.  describe.c got missed when it was renamed.
Bug introduced in commit 07cacba983ef79be4a84fcd0e0ca3b5fcb85dd65.

Andres Freund
Add a regression test case for \d on an index.

Previous commit shows the need for this.  The coverage isn't really
thorough, but it's better than nothing.