Allow multi-word "install" command.

Autoconf can determine that the correct install command includes flags,
e.g., "/usr/bin/install -c". When using this as a command, we can't
enclose the value in double-quotes, as that makes some shells use the
whole expression as a filename:

# this is the value returned by autoconf and stored in CT_install
$ ins="/usr/bin/install -c"

# if we call it with quotes, the command is not found
$ "${ins}"
bash: /usr/bin/install -c: No such file or directory

# removing the quotes lets it work as expected
$ ${ins}
/usr/bin/install: missing file operand
Try `/usr/bin/install --help' for more information.

Signed-Off-By: Anthony Foiani <anthony.foiani@gmail.com>

 # libelf config file

 choice

     bool

     prompt "libelf version"

 # Don't remove next line

 # CT_INSERT_VERSION_BELOW

 config LIBELF_V_0_8_13

     bool

     prompt "0.8.13"

 config LIBELF_V_0_8_12

     bool

     prompt "0.8.12"

 endchoice

 config LIBELF_VERSION

     string

 # Don't remove next line

 # CT_INSERT_VERSION_STRING_BELOW

     default "0.8.13" if LIBELF_V_0_8_13

     default "0.8.12" if LIBELF_V_0_8_12