Odd problem in AC_PROG_INSTALL

[Tim Van Holder]

I just noticed I neglected to use AS_EXECUTABLE_P and
$ac_path_separator in AC_PROG_INSTALL (I used to set
$INSTALL in config.site so hadnt yet run into this).
Trying to add it yielded strange problems: configure
keeps complaining 'test -x: command not found'.
The really odd thing is that 'bash -x configure' shows
the following trace:

+ echo 'configure:971: checking for a BSD compatible install'
+ echo 'checking for a BSD compatible install... \c'
checking for a BSD compatible install... + test -z ''
+ test '' = set
+ ac_save_IFS=

+ IFS=;
+ 'test -x' E:/Djgpp/Bin/ginstall
configure: test -x: command not found
+ continue
+ 'test -x' E:/Djgpp/Bin/scoinst
configure: test -x: command not found
+ continue
+ 'test -x' E:/Djgpp/Bin/install
configure: test -x: command not found
+ continue
+ 'test -x' D:/4Dos/ginstall
configure: test -x: command not found
+ continue
+ 'test -x' D:/4Dos/scoinst
configure: test -x: command not found
+ continue
+ 'test -x' D:/4Dos/install
configure: test -x: command not found
+ continue
+ 'test -x' C:/Windows/Command/ginstall
configure: test -x: command not found
+ continue
+ 'test -x' C:/Windows/Command/scoinst
configure: test -x: command not found
+ continue
+ 'test -x' C:/Windows/Command/install
configure: test -x: command not found

coming from

  AS_EXECUTABLE_P("$ac_dir/$ac_prog") || continue

which is EXACTLY what AC_CHECK_PROG uses.

Using

  if AS_EXECUTABLE_P("$ac_dir/$ac_prog"); then

as AC_PATH_PROG does yields the same problem.
I'm at a loss as to where the quotes come from; as
far as I can tell they are never added, and they
don't show up anywhere but inside AC_PROG_INSTALL.