Update Ubuntu Install Comments

Changes:

 * scripts/install-dependencies-ubuntu.sh
U#   (use "git add <file>..." to include in what will be committed)
Refactor Install Response Processing

Factors the code that tests for yes / no responses to install questions
out into a function. Replaces all instances with the function.

Changes:

 * install.sh: Add is_affirmative function and use it everywhere.
Add Install Warning Message

Adds code to print a message informing the user what the install script does
and that it may not be the right choice for every system.

Changes:

 * install.sh
Implement CentOS / RHEL Dependency Install

Adds a script that installs the dependencies needed to build PerfTrack
on CentOS, RHEL, and other RHEL-based distributions.

Changes:

 * scripts/centos-pg_hba.conf: PostgreSQL config file that allows MD5
   authentication for local clients. Used to replace CentOS config that
   only allows ident access.
 * scripts/install-dependencies-el.sh: Dependency install script.
   Installs development packages, Postgres, python modules used.
Add Space Before Finall Install Message

Adds a space to the here-document that prints out the message at
the end of install.sh to separate it from the cmake output that
precedes it.

Changes:

 * install.sh
Update EL Install Header Comments

Updates the comment header in the Enterprise Linux dependency
script.

Changes:

 * scripts/install-dependencies-el.sh
Rename PerfTrack Path File

Renames the PerfTrack Python .pth file in the source prior to adding
a generated path to it.

Changes:

 * src/perftrack.pth -> src/peftrack.pth.in
Generate Contents of Python .pth File

Adds code to the CMake config to insert the appropriate path in the
Python .pth file for the PerfTrack Python modules. Additionally,
attempt to install the .pth file in the top-level site-packages
directory so that the modules are found on RHEL / CentOS after a
default install.

Changes:

 * src/CMakeLists.txt: Generate the contents of perftrack.pth file.
   Attempt to install the perftrack.pth file in the top-level site-
   packages directory.
 * src/perftrack.pth.in: Replace contents with the CMake variable
   for the PerfTrack module path.